Am I over reacting?

So after getting married and having a kid I found out my husband cheated while I was pregnant (we dated for 4 months at that point but I was 3 months pregnant..I know I know..

After I found out about this I asked if he felt bad what went through his stupid head?

And so many other questions

He tried telling me that the girl..ex gf he cheated on me (phone sex) with was trying to mess up our family because she’s the one that let me know about the whole cheating scandal. And I was like wtf it’s 100% your fault she had nothing to do with being unfaithful she’s not in our relationship plus she didn’t know about me. And he’s the one that called her.

Today I brought it up again and he ended up digging himself in a bigger hole in my opinion he told me that she was 10% at fault because she would’ve done the whole cheating thing even if she knew about me. And I let him know that I don’t care if she would’ve done that that’s her business the thing is that YOU were the one that came up with the idea to contact her knowing she didn’t care if he was in a relationship and ended up cheating on me.

And he also mentioned that we were only bf/gf at the time, I was 3 months pregnant as well (he proposed a week later)

Am I going crazy/overreacting or is he just stupid?

What would you honestly do? (We have a kid)