relationship🤷🏻‍♀️

I don't usually post on here I only read the comments but 2 days ago my boyfriend rang me while claiming he wasn't drunk which he was and accused me of cheating on him with my boy bestfriend. While he was accusing me his mates sister  rang me off his phone and also accused me even though she doesn't know me. After he had left the friends he was with he was constantly ringing me texting me asking me if I had done it (ild never and would never cheat on my boyfriend or anyone for that matter) I told him I haven't and that he was drunk and he had to go home, he then told me that he loved me and that he still wants to be with me blah blah bullshit. Since that he's hardly spoken to me, making me effort to apologise, claiming he doesn't know what to say to me. Funny thing is I see a message on his phone to his friend that he see 'the girl' who he fucked in Lincoln while away with friends for a lads birthday. we've been together 5 years and I haven't mentioned it because I want to save our relationship and I look the bad one for going on his phone. I just don't know what to do!😞😞 it's messed up!