Need advice

My fiance and i have been together almost 2 years now. We have a beautiful 3 month old daughter. During my pregnancy i was unable to have sex per doctor orders (i had numerous complications). He would go on facebook and message his exes. Most of tge messages were just flirting but at one point he asked for naked pics. I confronted him each time i found out and told him how much it hurt me. He said he just needed some attention and it wasnt cheating. All of these women live in a different state so its not as if he could actually hook up with them even if he wanted to. I still consider this cheating and told him after the last time if he did it again i would leave him regardless of the fact that we have a child together.

Recently he has been messaging a girl he hooked up with 4 years ago about the possibility of her daughter being his. While i definitely think thats something he should find out the way he was talking to her made it seem like he wanted more than that. He was saying thjngs like how he missed her (they were friends who hooked up at a party). And that he wanted a second kid so bad. And just kept mentioning over and over how they had sooo much sex that night like he was reminiscing. She told him she got her period afterwards and she was hooking up with 2 others guts during her conception window who she thinks is the father. So he tells her he researched and that she could have had her period and be pregnant and that he just wants to be there for his family.

I cant even get him to read a couple pages in a baby book about how to prepare our daughter for bed because he "hate reading". He thinks im overreacting. He says i shouldnt make a big deal because it wasnt like he was flirting her or asking for naked pictures and they were discussing something that happened 4 years ago.

I also just want to say im not one of those girls thats just goes through his phone alk the time to see if he cheating. He leave his phone lying around with the messenger open where i can see the messages without even touching his phone. But he tries to make me feel like im crazy for looking at them

I just want to know if im in the wrong here for 1 reading his messages and 2 making a big deal about him talking to this girl