Internet friendships tend to be sort of "otherworldly", an altered perception of reality through the lens that's created there, and I think that many times people don't consider how altering it is. Hence so many get their heart broken over how reality doesn't match up, and yet others make the mistake of thinking that it's not reality at all and that their experiences there are all just harmless innocent fluff.

I've been on both sides of the fence, in a sense; I was married to someone for many years that I met on the internet -- which was much weirder at the time (late 80's), when far fewer people were interacting online in far fewer ways, and with less social acceptance -- and then long after we had split, I accidentally caught a subsequent partner trolling for tail on POF (I was doing a copy and paste on the computer and must have mis-struck when I went to copy, because when I went to paste I got a boilerplate introduction paragraph of his reaching out to women he'd never met before, "hey, saw your profile and you look adorable, we should meet" bla bla bla that sort of thing), and we were not together for very long after that.

My best advice if trying to work things out with him would be to keep a healthy open dialogue, hard as it may be at times. If he's communicating openly about it, at least you are less likely to be surprised by developments.

However, having read your 2nd post in this thread I have to say -- any person who uses the other's mental health concerns as a lever in arguments just to get their way is really bad news. That's crazy-making, and it is not allowed. Good riddance if you broke up with him.