Cheating on his gf with me

So recently I started hanging out with this new group of friends and I got closer to this one guy. One night a few of us got together and me and this guy were left alone. We started talking and still acting like friends. He asked me if I wanted to make out with him but, I asked about his gf (because he has one) and he said that she doesn’t have to know. I thought about it and I said yes and we started making out until the rest of the group came back (which wasn’t that long). The next day we hung out again and this time we were making out the whole time and got really touchy with each other. I feel guilty that he cheated on his gf with me but, he has cheated in the past. I’m not sure if should continue to mess around with him or if should cut it off. I don’t really have feelings for him but even if I did he would cheat on me. Should I just tell him to lay off.🤷‍♀️