Cheated Months Ago!!

My fiancé and I went on a break when we had been together about 10 months. He was gone for a few days and came home, but I found out there was this girl he was hanging out with but I couldn't really be upset because we weren't actually together. So I let it go, or at least tried to. Fast forward, we've been together for two years and I'm 27 weeks pregnant. I've been having dreams about when he left and about the girl and stuff every night for over a month. So finally, I asked him about her. I wondered if the dreams would go away once I knew the whole story. Turns out, they had been talking since before he left! And continued a little after he came home! AND there was another girl he was talking to, too! And I found out that, during the break, he kissed her. I asked why he came home & why it didn't work out with the other girl. He said "I missed you and she just didn't compare. She wasn't what I wanted". Idk how to feel. I've honestly been pretty numb to the situation all day. (We talked last night). I cried a lot last night but haven't felt anything toward it or toward him all day. Am I overreacting? I feel like I'm not reacting at all and I don't know why. Help me 😞😓