I am sorry.....and...I am going to be right up-front with you. I don't think he is the only person in this relationship that needs help. I beleive you may have a self-esteam problem and the reason I say this is because you really have no ties that bind you to this person but you keep coming back for more. Love isn't allowing people to call you names or make you feel worthless. You also mentioned that he seems to be getting worse which means that he needs help that you really can't give him. Disability or no disability you deserve to be treated with respect and stop allowing this guy to utterly disrespect you.
As far as you having no one around, I think I would rather have no one then someone who acts the way that this person does. You have to know that there is more to life then what you are getting now. I would back away from him...running backwards if necessary and seek some treatment for yourself. (sorry...my opinion)