Need help😭found his dating apps

I’ve been with this guy for 7 months now. Everyone knows me as his gf but we never talked about it until recently. He says if I want monogamy he wants it too but said it very unwillingly. I have major trust issues and he knows about it. He says he doesn’t know how to show or prove how much he cares about me. I see his family every week and go on vacation with them. He swears that he doesn’t talk to anyone else and hat I’m special and he loves me but he’s been sleeping with or at least talking to girls online the whole time. Messages were like “are you free this week” “are you on birth control” “are you a freak or into bdsm” etc. calling them nicknames he calls me. He doesn’t know hat I saw all this. I would leave him but he’s such a smooth bullshiter and I feel guilty that I saw his phone. How do I leave him??