Fixer, my heart goes out to you, your son and family.
I think you are absolutely doing the right thing in controlling his interactions with your family to outside of their home. You have to have a safe space for everyone else to be able to stay calm and deal with the problems he is causing for the family, and to heal your own stress and upset over this.
Having read the rest of this thread...I see some red flags and feel the need to comment further, for the sake of my own conscious. I have to say it seems very clear to me that you are describing someone who has a dual diagnosis at the very least. (More than one diagnosis to handle at once). What you are describing is not typical of someone with Asperger's syndrome, to my training and experience. Not saying he doesn't have Aperger's just that more is going on with him than that....which needs to be addressed first.
He is self medicating with drugs (over reliance, over use, getting more than one prescription, etc.) and alcohol. A twelve step program like AA or NA might really help give him much needed structure and support, and encourage him to work a program. I urge you to find him a substance abuse counselor and program to work with. This might be key to his recovery.
He clearly has an impulse control problem, and if he has been compulsively stealing things, money and stuff, you are absolutely right to deny him access to your home, just as you would any other active addict. That he may have some other mental/emotional problems at work in his life is NO EXCUSE for the bad behavior of lying, stealing and drug and alcohol abuse. He has to (and can) take responsibility for those. Including cooperating in handling whatever legal troubles he is in because of his substance abuse. Here we have drug courts, which largely do diversion for first time offenders into treatment. He may need re-hab (substance abuse treatment in a lock-down facility) more than he needs psychiatric treatment...does he hear voices? Feel compelled to do unusual repetitive actions or rituals? Does he go through periods of missing time, have black-outs or where he is really out of touch with reality, or hallucinating? Any of this visible or obvious to other people? If so, then he definitely needs psychiatric care as well.
A lot of young people who have some kind of mental/emotional illness or just have a lot of stress and anxiety from dealing with a learning disorder which is not being treated adequately turn to drugs and alcohol to self medicate...it sometimes helps them for short bits, but always creates other bigger problems in their lives as well. He is not alone if this is primarily what he is doing... I wonder if your son has also developed some kind of an substance abuse/addiction problem, in which case he could really benefit from some specific treatment from a substance abuse counselor (someone trained to handle those issues), in addition to medical treatment for his anxiety or any other mental/emotional or social issues. Even more so than from psychiatric treatment, at least initially.
Most people with Asperger's syndrome have normal to very high intelligence, but seem to be socially handicapped. Their difficulties are in fitting into society and in understanding other's emotions, "reading" people right, seeing how their own behaviors effect others, and in communicating well and in getting along well with others. Like people with autism, they are often anxious, sensitive to the point of being easily upset and highly reactive to unpleasant outside stimuli. Loud noises, certain smells, textures of clothing, windy or stormy weather, some tastes and textures of certain foods grate on their nerves far more than neuro-typicals (and hey, we're all on a spectrum here! Some of us "normal" people have nerves of steel, some of us are a little jumpy, and some of us are really sensitive).
I have to say that many of the traits you are describing sound to me very much more like a Bi-polar (what used to be called manic depressive) disorder or extreme ADHD, and not so much Asperger's syndrome. It is possible for him to be on the Autism spectrum and also have an issue of being Bi-polar, ADHD, or a substance abuser. Each of these would need to be treated in their own light.
You mention he was on an anti-anxiety med (which he was ODing on in an attempt to make it "work" better) and then they put him on Lithium, which is almost always specific for Bi-Polar disorder. Garden variety depressives with anxiety issues seldom if ever are put on Lithium...(Aspies never are) usually either anti-depressant medication or anti-anxiety medication works well for them and normalizes their behaviors and enhances their coping mechanisms and functionality. That these have seemingly not worked for your son tell me that something else is at work in causing some of his more extreme behavior, mood swings, lying, impulsively acting out, etc... It sounds as if they are treating him for bi-polar disorder, which is an entirely different diagnosis from Asperger's syndrome. He is clearly not in control of himself yet, and needs a lot of structure, oversight and support as his doctors are finding the correct medication to help stabilize him.
I myself do not think that Asperger's syndrome by itself is a mental illness, more like a form of learning disability... their brains are just hard-wired differently from most, it doesn't made them mentally ill... although when I was first in college being educated about this, and ADD (attention deficit disorder) and ADHD (attention deficit hyperactivity disorder), they were described as being "minimal brain damage" or "minimal brain dysfunction", which is a neurological deficit issue and not an mental illness.
As you are doing some research, please look into and learn a little bit about these two conditions, ADHD and Bi-polar. To my experience, the kinds of actions you are describing your son has been taking are more typical of these, and not so typical of Asperger's syndrome. I'm pretty sure there is more going on with him that just Asperger's. ADHD and Bi-polar disorders often run in families. From your description of his Mom, she seems to clearly have an anxiety disorder herself, at the very least. Possibly she also has Bi-polar disorder or ADHD issues as well as your son does, and has never been treated adequately for them.
You and your entire family (without the son) can benefit from some family counseling (just talking therapy) to help heal from the distress of all this and also to help shore up your healthy boundaries with him and each other, and to move forward in a positive way together. See if you can find someone trained in Cognitive Behavioral Therapy, and experienced with family systems issues. All of you need some relief and support and care, too.
I don't want to sound negative in any way, but feel that it is realistic to share that he is at the age when Schizophrenia often shows up in males (early to mid twenties). This also tends to run along genetic lines. If he is really such a good lier, he may also be lying about what his symptoms really are, as well, even to his doctors. It may be useful to his doctor(s) to know that his biological Mother also has (at the very least) an untreated anxiety disorder.
One thing that may help you to decide what it is, is this...people with Bi-polar disorder often in their "manic" (emotionally, energetically "high"phases) are highly sexualized...overly so, at times, which may show up as heavy, heavy focus on the girlfriend or significant other, (or in searching for a partner) obsessive thoughts about love and romance, unrealistic expectations from a relationship, and a great deal of time, energy and focus spent on sex and pursing sexual encounters or love and romance. Does this in any way describe your son's behavior, or your ex-wife's? (You don't have to answer here...just think about this and answer to yourself)
I just went through an intense and grueling time dealing with a person who was struggling with a mental illness, who had survived a serious suicide attempt. I was brought into the family situation just after she was released from the hospital. She is now doing much better, living in a different, supportive home, moved on from a dysfunction and unrealistic romantic entanglement and has a whole team in place to support her needs. The mental/emotional issues will need to be treated and addressed for the rest of her life, but being in a safe and supportive environment makes it all so much better. I would say, try and get your son into rehab, if possible (the in-patient kind, where he graduates to a halfway house or group home, still somewhat supervised. He absolutely should NOT be living independently at this time, until his illness is better treated and he is more stable).
As someone who has experience working with people who are sometimes suicidal, I can say that more often than not, it really is a "cry for help", and that those who attempt suicide do not really want to die, but are just in such overwhelming pain that they cannot see any other relief in sight, and just want the pain to stop. This is the best, easiest way that they see in the moment to make that happen.
I would say that neither of your son's two overdose experiences strike me a serious suicide attempts, although he may be flirting with it and needs intervention about it.
For the benefit of everyone reading here: a serious suicide attempt versus merely "acting out" with threatening suicide, a practice run (which happens more often than you'd think), etc. is this:
In a "serious" attempt, the person will go where they cannot be found, where they will be left alone, where they are not in touch with others, are not known, etc. For someone to immediately call another person and tell them what they did, or do it where they will be checked up on, or found (in time or not) etc. is more of an acting out, or a mistake in self-(over) medicating, as what happened with your son the second time. People in manic phases think that they can drink and take drugs and it won't really hurt them...often they feel kind of superhuman, in an irrational sort of way, don't eat normally, don't sleep normally, etc. Also, some young people, teens and tweens, have a kind of magical thinking about death sometimes, so that they will act out in the home and feel that someone will "know" and will come and stop them in time, etc.
To drink and OD, then call someone (your girlfriend or other close caring person) is more a messed up form of acting out, an attempt to control out of control thoughts and feelings, an extreme attempt to self medicate, than a serious suicide attempt. The problem is, people do sometimes accomplish death under these circumstances. Usually it is just a cry for help, and anyone who is doing this should be in a facility where they can get round the clock care and observation until their meds are straightened out, and their thinking and behavior becomes more normal. In an ideal world.
Fixer, feel free to pm me if you have any questions, or if you need to talk. I am at your disposal. Perhaps I can help with researching some resources for you. The multiple issues with your son sound very challenging, and I want to give you some support. He needs a team, not just his Dad, advocating for him and finding him proper treatment. You and your family need some help and support, too.
First of all, it's important to understand and to research and learn about what his true diagnosis (es) are. If they've got him on Lithium, his main issue is NOT Asperger's syndrome. He is probably not a reliable reporter of what they have told him or what he is experiencing in treatment. He may not be taking his meds properly, or eating and sleeping properly (without which the meds will not really work right). Most people are ashamed when they get a diagnosis of mental illness and try and minimalize it or lie about it, deny it or call it something else (sometimes for years). This is a pretty "normal" defense mechanism. Try to break through this denial if you can. I realize how very difficult it is for non-Scientologist families to do this, so I imagine it might be even more so for a family influenced by Scientology beliefs about mental illnesses and their treatments. Big hugs to your whole family, including your ex-wife.
Once again, my heart goes out to you and to your son. Don't give up on him. Does he have a social worker overseeing his case? If not, it's probably appropriate to contact Adult Protective services or Mental Health department, or Social Services for wherever you live, and request that they open a case file on him. At twenty-six, he's not a kid any longer, and his problems are serious. He needs a "team" on his side, not just you and your family and his girlfriend.
People can and do recover from much worse things than this. Courage!
. It's more than I can get locally, even the psychs are hard to get hold of. I'm still waiting for contact.
No shock treatment 
", etc. 
