Dating sites

So I caught my boyfriend talking to girls on dating sites without my knowledge. Receiving nudes, sexting, etc. I was open to threesomes when we got together, under the condition we talked to girls together. He was talking to these girls behind my back. I confronted him, and he said I could look through his phone. When I got the chance to, he had deleted all the chats, even after he said he never deletes anything (he usually doesn't). Then randomly he has me text someone on his phone, and I notice him talking behind my back to one of the dating site girls, so I look at it and apparently when he was driving through he went to her house?! I confronted him and he downplayed it, said they just talked. I'm pretty sure he's lying. So I told him forget it I don't want a threesome and I asked him to delete all those girls. He said he did, and then I find him talking to them again and he made up some dumb excuse like checking up on their cps case they told him about or whatever. I feel like he doesn't think I'm enough since I had our baby, and I've caught him cheating (the texts and stuff) and I'm pretty sure he hooked up with that girl. Am I overreacting? I don't even know how to talk to him about how I feel