Why are you on a break when he cheated on you? Perhaps I read that wrong, but then, why are you getting back with him at all If he's just gonna move on and have sex with someone and then try to hide it from you?

Girl, you need to make like a tree and leave. Drop him like a hot potato be before it's too late.

You're better off alone than trying to be with someone who won't try to be with you. I suggest just leaving him.

If you are on a break, there is no reason to be mad if he is sleeping around since you aren't in a relationship with him. Though why would you so stupid to be on a break with a guy who cheated on you? You deserve it for keeping that in your life.

You have to see there is no future in this - you are just making it worse on yourself by being around him (being roommate to your ex-! That's madness!). It's Christmas - make like a shepherd & get the flock out of there.