Sorry if this is long I appreciate anyone who takes the time to read and comment I am at a loss as to what to do right now and completely heartbroken please share what you think I should do

Tonight I accidentally saw something on my boyfriends phone as he was scrolling through, I straight away asked him to show me, it was a kink dating app and he straight away lied and said it was to "show his co workers" after which I demanded to see, he got all flustered said he will show me later, I said no right now as I knew he will delete, he tried to uninstall the app but I took the phone and opened it at which point he just let me and I saw he had been talking to many women, I scrolled down and saw atleast 20 but could easily be more.

Opened a few messages, basically to every woman he said that me and him are looking for a threesome together, pretending im in on it and completely okay with this. He has told them intimate details about our sex life, even in details of exactly what happened last time we had sex. The women seem to have been getting themselves off to his messages and even writing him dirty stories for "him and me" to read together. He also told a few women that he's my master and im his slave and he needs someone to help him "break" me in. While we have interest in dom/sub dynamics I have never agreed to being a slave or for him to do any of this. With all women he claimed that we both wanted this. He told a few that "they would be perfect for us". There was a lot of other sexual things and messages from women describing how theyre masturbating but I just couldnt read it all as there were too many of them.

He says he never got himself off over/with these women (not sure I believe that) and that this is just a fantasy and he never would have done anything physical. He says this isnt cheating because it was only over the phone. This has apparently been going on for a few months now. I really dont know what to do. I told him to take his things and leave tommorow morning. I feel so awful that I wasnt enough for him and he felt the need to look for other women and play out these fantasies with them. What do you think I should do? Would you consider this cheating and would you stay?

Thank you so much to anyone who came this far and leaves a comment ❤️