am i a monster? what do i do😭

i've been with this guy for about a year. i've given him 3 chances so far. he would have other girls in his phone (snap, ***, ***, and i found hinge and bumbl). he also physically cheated (confirmed) one time, but i have a feeling it was more. i actually texted one of the girls who he was texting under an unsaved number, and she confirmed they were kind of emotionally cheating. he sent her money and called her babe and stuff. this happened with another girl too. i just kept giving him chances, and now i've become someone i wish i wasn't. after the last chance i told myself i would break up with him, but i let it happen again. i'm not strong enough to end things, so i just resorted to treating him how he has been treating me. i downloaded hinge and have been hanging out with other people, going on dates, and im not going to lie, i've had sex with one of them. i turned into the cheater myself and it's killing me. i thought it would make me feel better and that i wouldn't care since he did it to me, but it's KILLING ME. i feel worthless