I need advice.

So I've been with my husband for almost 2 years. and we've had an alright relationship for the most part. but tonight really sent me over the edge. he said he was going for a walk and all of a sudden he pocket dialed me and I heard him saying " I want that old thing back, I wanna eat that pussy" I miss that shit. and I lost it. I literally felt so hurt. come to find out it was his baby mom he was saying that to. I called him back and flipped on him. her says he only said that so she wouldn't put him ob child support. and I'm supposed to be okay with that. because he said he's not really gonna do that. I'm also 7 week pregnant And have a 4 month old with him. am over reacting because i want to leave???