Sorry this happened to you. I heard a similar story from a friend recently, that his brother invited his (the brother's) ex-wife to move back in with him. My friend warned his brother it was a mistake, the brother didn't listen, the ex-wife moved in...and they're fighting again, like cats and dogs. The ex-wife is now on the lease and the brother will probably have to move to get rid of her.

Some possible advice, moving forward, is that for the duration of your time together, keep a detailed journal about it. All the annoyances, nasty comments, fights, conflicts, etc. And when you're separated from him again, reread it anytime you find yourself tempted to reconnect.