I don't even recommend being roommates with friends, because it can really test your friendship. It's easier to be roommates with strangers because there's no expectations and you don't know them well enough to expect anything from them. You'll eventually become friends. I have one ex and I have no contact with him whatsoever, I don't know how you could do it.
Right now, I live with my boyfriend, but we share the apartment with his old roommate and his girlfriend. My boyfriend is friends with the guy, but I can't stand him. I think he's so inconsiderate and irresponsible and can be a jerk sometimes. It sucks to have to live with him, but I mostly keep to myself. I'm polite if I need to be, but I don't like socializing with him. My boyfriend knows how I feel too, but since we both don't make much money to live on our own yet, I just have to deal with it. I just wait for the day where we can live on our own. I either am too busy with work and school to be bothered by the guy, or I'm in my room catching up on lakorns and Kpop stuff. The best thing is to just keep to yourself. You can ignore someone enough to where they'll just stop trying to be noticed.
Or, find someone to replace him. Tell your roommates you can't live with him anymore, and if he's at all a decent guy, he'll leave. He is the guy after all, he can't be thick skinned and live with someone that doesn't want him there.