Cheating

So I was out with my two best friends yesterday at the Mall and we were all talking at one point about our boyfriends and where they lived and who they were and how nice they were.. long story short.. I found out that one of my friends was talking to my boyfriend in December not even two weeks ago and we were together since October.. he said he was single and was best friends with my friends cousin. Anyway the cousin gave my boyfriends social media information to my friend they started talking she wasn’t into it he was totally flirting talking about sex, are you a freak etc. I confronted him about it that same day and he said that my friend was his best friend, and that he never flirted with her.. through all of this we had everything from the conversation like all screenshots.. anyways he told her cousin to lie for him so I would stay his girlfriend.. he lied straight to my face and I was talking to cousin to and we all knew that he was lying.. he blamed it on how he wasn’t texting her it was his friend on his phone.. but she said he sent pictures and we have screenshots of the conversation.. we talked it out last night but I still don’t know like what to do - he was totally crying on the phone saying how sorry he was but like I just don’t know what to believe like what else is he hiding from me ? so I just need your opinion on what do I do do I call it off or do I keep him..