Do I leave my boyfriend?

After a long day of running around I get a random add from a girl on Snapchat, which isn’t really out of the ordinary except for the fact we had no mutual friends but is something I looked past. I added her back and she immediately started typing and I thought that was pretty weird so I went onto the chat. When I saw the first message “Heyy girlll” I already had a bad feeling. She explained that about a month ago my boyfriend picked her up and brought her to his house and hooked up. She also was apologizing profusely because she didn’t know we were dating till she looked at his instagram profile and saw the highlight of me and him together.

I called my boyfriend right after hearing about everything that apparently happened. When I told him he started saying that nun of it was true. A big factor that I should point out is that he has recently cheated on me, another girl had messaged me saying that he and her were talking but she had no idea he had a girlfriend. After I found out the first time I made him give me all his social accounts, instagram, Snapchat, TikTok, etc. But this girl is saying that this happened before he gave me all his socials. Anyways he ended up sharing his screen to me as he texted this girl saying that he had no idea who she was and why she would be lying to me about this, she was confused saying that the power had went out and he had to charge his phone so he came over and then later brought her to his house to hook up which to he all denied. He also said that he had never added her and as proof she sent a picture of their friendship pfp saying that it had gone up 30 thousand since she had last had him added. So he lied about never having her added. Overall I just don’t know who to believe.

Im supposed to be meeting his family for the first time in 6 days for his birthday so I need to get this figured out before. So what should I do, do I break up with him or should I believe what he is saying and stay with him?