I’m pregnant and I think I caught my bf CHEATING ...?!?!

So I was having a conversation with my boyfriend about how he’s barely been emotionally present in our relationship ever since we found out that I was pregnant. I’m now 5 months pregnant with my first child. For a background I am 28 and he is 22. In December his hours at work weren’t quite adding up and I asked if he was seeing someone else. He said no and tried to explain away the whole thing. I took him at his word and just decided to quietly monitor the situation because my gut told me otherwise.

Fast forward to tonight where I finally snap and ask him to open his phone with my room mate in the room to play counselor because she keeps me in check and tells me if I’m over reacting. After his Snapchat going off at all hours of the night when he’s home I decide to finally take a peek. I hand the phone to my room mate because I needed a buffer and as she’s scrolling reading his messages she’s asking for clarification on certain messages between him and this other girl he works with. She’s apparent an old “friend” from high school. They had been talking back and fourth about her being sexually frustrated and him telling her to masturbate and send pics or it didn’t happen. Then he would send her shower pictures and message her while in the shower. They talked about how he would tease her at work by pulling her hair to get her horny and she mentioned how good his dick felt in her hand.

He denies that anything physical happened and says she was referring to high school days when she blew him under the bleachers. But my stomach is sinking over this. He said he just thought it was innocent banter and play. But my point is that once it turns sexual in nature it is no longer innocent. Towards the end of the messages she blatantly asks him to fuck and his response was “lol sorry”. I’m so sick over this I don’t know what to do or even if I actually caught him cheating or some other version of the word. I never thought I’d be facing being pregnant and not being able to trust my SO or having my relationship on thin ice.

What should I do? And did I actually catch him cheating? And if this other chick new about me and still did this and is still working with him then what?