Cheating

So I know this is going to be a long post, but I just need someone’s opinion. My boyfriend and I are not the jealous type at all. He has female friends I have male friends and there is never any issues. Until this one girl ( who we will call Becca). Becca was his best friend for years and I LOVED her in the beginning. Now as I said my SO and I were never the jealous type but this one day I just had a gut feeling that something was wrong. So I went through his phone and In Becca and his messages she was talking shit about me and he didn’t stick up for me AT ALL. She was making comments like “oh did you dump her yet lol” and “do you actually even like her now”. We got into a fight at his birthday party because she was all over him and he didn’t see it and I felt like a fool in front of all those people. Becca texted him saying that I ruined the whole night (she didn’t know why I was upset, nor the reason he was because we didn’t fight about it in public we kinda waited till we were home). On top of all of that he was texting her saying that her friend ( we will call her Sarah) had a fat ass and was so hot and was calling my friend (we will call her Brianna) was so hot. HE SENT BECCA MY NUDES TO RATE THEM ON A SCALE OF 1-10 AND SHE JUDGED ME AND HE MADE FUN OF THEM WITH HER. For my birthday this past year he took me on a trip and I guess him and Becca were texting the whole entire time and he was telling her that he was still unsure if he liked me. And then Becca had the audacity to say I was jealous of there relationship????? I flipped out on him and we really haven’t been the same since. I’m just not sure if it can be fixed or not. He tried to tell me that he didn’t mean anything that he said and that he loves me and would do anything to prove that. But how am I supposed to forget about all of that?

EDIT: ON TOP OF ALL THAT SHE USED TO SEND HIM LINGERIE PICS THAT SHE WOULD BUY FOR HER BF AND HE WOULD TELL HER HOW HOT AND SEXY SHE WAS BUT IF I WORE IT FOR HIM HE WOULD CALL ME A CUTIE.