How do I know he's really changed?

I divorced my ADD husband 10 years ago. We remained in touch because of the kids, and now the anger and pain have cooled and we are good friends. He wants to move back in with me when he retires in a couple of years. We have fun together and get along well, but ONLY because he doesn't live here and I put no pressure at all on him. When he stays the weekend (he has no interest in any kind of intimacy), I think of him as a guest; if he does some thing to help out (he likes to cook, and does a few repair jobs) I thank him. HOWEVER, if he moves back in, I don't want a permanent house guest; he will have to have some responsibilities, and that's where the trouble will start. He swears he's changed, but how can I know? He still does irritating things like interrupt me mid-sentence.

Every time I seriously consider letting him move back, I have nightmares of all the pain and misery..I wake up crying.. How can I get over that? How can he prove that he's changed before he gets back into my house (last time it took a year to pry him out). He won't discuss the past, and thinks we should just forget everything that happened before (it's etched into my mind; I can't forget).. If I bring up an incident, he doesn't remember it, or remembers it differently than I do, and just says "If I did that, it wasn't intentional". If he doesn't remember the past, takes no responsibility for it, and has that disconnect between his intentions and actions, how can he change? How can I trust him again? Should I ever trust him again?