He's cheating on her with me

Okay so me and this guy hooked up a few months ago but we never really fucked a month later I found out that he had a girlfriend all along.. It's been like 3 months and 1 week ago I was drunk and we fucked and I go on his ig to see if he's still with his gf and he is and I kinda knew in the back of my head but idk what to do anymore bc he's always hitting me up to fuck but I feel like I'm gonna develop more feelings than what I already have for him and he has a gf, I feel like every time he hits me up its so hard to resist and say no and I hate myself for it,  any advice ladies? Please don't judge