Cheating or not ?

So me and my ex boyfriend broke up late October but we still talk and text see each other and have sexual intercourse ..I recently just met a new guy at work and we just clicked we started texting talking and etc then he invited me over and eventually had sexual intercourse and we still talk and text too now my ex boyfriend is thinking about getting back together and says that we’ve been in the talking stage now for a few weeks ..should I tell him what’s going on ?? And the problem is I’m actually feeling them both someone help