Need helpšŸ˜­found his dating apps

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Iā€™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 doesnā€™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 doesnā€™t talk to anyone else and hat Iā€™m special and he loves me but heā€™s been sleeping with or at least talking to girls online the whole time. Messages were like ā€œare you free this weekā€ ā€œare you on birth controlā€ ā€œare you a freak or into bdsmā€ etc. calling them nicknames he calls me. He doesnā€™t know hat I saw all this. I would leave him but heā€™s such a smooth bullshiter and I feel guilty that I saw his phone. How do I leave him??