Found out my boyfriend is cheating- how should I confront him?

So my boyfriend and I broke up for awhile and just got back together a few weeks ago. I never had any trust issues with him before but since we got back together he's been kinda hiding his phone and I saw messages on a few different occasions from this girl, and he always quickly cleared the message. A few days ago he was showing me something and I saw a message from her asking what his address was (so she could come over?) So I asked him about it immediately and he hesitated and said she was a friend then quickly changed the subject, obviously lying. So when I got the chance (I know I shouldn't have) I looked through their conversation. From what I gather they haven't done anything physically but he asked her to come over several times, saying that he wanted to fuck. It's killing me not saying anything. I want things to stay calm, I don't want to freak out on him or anything. But I don't know how to go about it. I don't get why he would do it because he was so faithful before and I'm helping him out so much. He's going through a rough patch and I've been letting him borrow my car for work and I've been paying for like 90% of his food and making sure he has what he needs, yet the entire time he was trying to fuck someone else. How do I talk to him about it while keeping calm?? I was thinking that if he stops talking to her that I'd give him another chance because we just got back together? But idk if I should. Sorry for the long post, thanks for the help