My boyfriend cheated

Girls I need help, I had a baby last year. He doesn’t live with me, so I’ve had such a tough time trying to get through that, the babies dad cheated on me multiple times before/during/ after I was pregnant so I thought I’d never trust anyone ever again. until, me and my partner got together, he was everything I needed, he made me happy again, he keeps me stable. I haven’t got a very good family so I rely on him a lot, anyway he has a baby aswell (not with me) and when we was about 3 months into the relationship he told me he still has feelings for his ex (the babies mum) so we worked through it and we were happier than EVER!! but the other day this ex sent me screenshots of them two talking, aka he has been having sex with her for ages and hasn’t told me, I love him to pieces and I’m not willing to lose him, but I’m confused and I don’t know what to do?!! We have talked about it and he has begged me not to leave and he has admittedly said sorry a lot of times, I just can’t stop thinking about it, any help/ stories 🤦‍♀️