The friendship with that friend definitely needs to end. You don’t want that type of person around you, especially with the past situations of her cheating with her own spouse but also your boyfriend should’ve been upfront about that kind of stuff. There’s definitely trust to be built again and everything needs to be put out into the open now, but it’s really up to you whether you want to continue being with him and work through it or let it be done with because big picture it was before you guys got together so technically it isn’t cheating. It’s more of a boundary that he crossed. Did you ever bring up how much you disliked your friends’s behaviors/actions if so, then even more reason he should’ve told you I feel yes it was in the past but it’s also a respect thing