Do you  think it is weird to fantasize about your ex cheating on you?
It can be. Do you think he has done so before?
Yes, I do. He cheated on me when we were together for six months.
It definitely is a bummer to have been cheated on and I'm sorry. If this hurts so much, I don't think it would help to turn this into a fantasy.
I don't care what you are saying. I know he's lied to me many times and I feel betrayed but I don't want to leave him.
Then you have to decide what you want because it doesn't seem like he wants to stop cheating. And it is wrong for him to do that, he could give you an std.