Ex boyfriend drama long

So my ex boyfriend has been trying to friends and reconnect. He didn't like how we ended. He was yelling at me and slammed the door at me. Everything is good. I want us to be civil. So last week he wanted to hang out in the middle of the night he has asked me before but work got in the way. So I went. Skip forward he wanted me to suck his dick I told him no but at the end we ended up kissing.

Let me give you more details. Prior to going out I thought he had a girlfriend. When he was suggesting to give him a blow job I thought they broke up. So that's why I kissed him. After we broke up I blocked him on Facebook after the date I unblocked him. Then I saw him hugging a girl as a profile picture read his profile that's he's in a relationship. Check her profile the same thing. Soo they are together. He doesn't know that I know he has a girlfriend. He didn't know that I knew before the date. He's willing to cheat on his girlfriend. He did tell me that he was a booty call to some girls sooo he's a cheater? What should I do? Advice