Did my boyfriend cheat?

So I was snooping through my boyfriends phone and I know, I shouldn’t have been doing it but I did, I noticed this girl on messenger and she started talking to him and then out of nowhere in the conversation he told her to add him on Snapchat which I thought was crazy weird. So I went on Snapchat, and found their conversation, and they were talking, then I see her number, said to call him. Then she proceeded to say “thanks for staying up with me all night that was really sweet” then he responded with “no problem want to call again tonight?” Mind you, The day that he called her me and him were in a big argument..... I didn’t want to keep on reading but I did, I saw the good morning text messages and something along the lines of saying “oh I’ll make you pancakes someday”..... I lost it and I flat out told him what the hell was going on he proceeded to say that it was nothing more than a friendship and said that I invaded his privacy..... and that he was sorry.. I told him he was sorry because he got caught and went home.

What’s so funny is before all that happened he told me that he loves me very much and that he wouldn’t want to break up with me ever.... i’m bawling my eyes out because deep down I know he cheated... not physically but texting another woman... and it hurts a lot...

What should I do...