It sounds like you are relating to your son with age appropriateness. You said that you are baffled by your own actions or behaviors but given your background, I can sure see how you got there. I sure don't think you should be hard on yourself for caving in to the ex in the past. What has already happened is now over. I think the goal to remember is " Is doing what I am doing me going to get me what I want and need". It is your future and you deserve happiness and to be free from care taking for another adult man regardless of his diagnosis. He may not be that smart to think this all out but he is doing what has worked for him in the past. Your enabling him to continue is up to you (an observation, not a criticism). He is holding you hostage on the phone so he can vent???? I know I have done similar things myself and felt selfish for taking care of myself because of my background too. I have learned that these people will suck you into the sewer with them and their misery. In my honest opinion, it will likely get worse before it gets any better in dealings with him. He will have to up his game (even if its subconscious). It is not your job to assure that someone does not commit suicide even if he threatens and even if he attempts. If he actually completed a suicide attempt, it would NEVER be your fault.
Many men that are abusive never hit a woman, because other tactics work. When they do actually become physical, its because their tactics weren't working. (threatening, bullying, manipulating, begging, promising, verbally abusing, psychologically abusing) Im not saying that he will become physical, but if you set healthy boundaries for yourself and stick to them, he will likely become more frustrated and up his game in someway. I hope you have a support system and keep reaching out for the encouragement if you need it so that you won't cave in. We all have set backs and have to start over, but I am here, as well as many others to support and encourage you to take your life back.