I don’t know how to end it

Sorry for the long story. I’ve known this guy for nearly a year now but when we first met I wasn’t ready to start anything new so I would blow him off when he wanted to take me out. We would also flirt but he never made it obvious that he wanted anything serious or casual. Eventually he just said “I want to chill with you” (after a staff party) so we did and planned to see each other that same week. We went on a date and things were good, we were flirty and the vibe was amazing. We chilled after, listening to his music and just talking. He was so sweet and everything for a while, good morning texts, calling me to check on me. Side note: he got out of a relationship like 7 months before this so I didn’t think he wanted anything serious with me. Eventually we ended up having sex, at first I questioned it because I wasn’t entirely sure if I was ready for that just yet (I didn’t want to have sex for a while). A key thing, we NEVER set boundaries ( I know I f’d up there). There was a situation where one of his friends (I’m also friends with him) came to mine after a party but NOTHING happened (this guy has been in a 6 yr relationship but is a known cheater). I told him literally the next day and I could feel his energy change with me (understandable, I’ve held my hands up and said I messed up there). Around this time a new girl came into the scene (beautiful girl btw) and when me and him would lay up after sex he would talk about three somes (something I would personally never do) and her name would come up but he’d also say he’s not attracted to her and doesn’t get the “sex appeal” thing with her. Eventually me and her actually became friends but she didn’t know anything that was going on with us. she came up to me one day and said he was flirting with her. I confronted him and he said I’m not his girl so it shouldn’t matter (fair enough but out of respect he shouldn’t have done that). A situation happened before this and I told him I was annoyed that he didn’t communicate that he had changed his mind about coming to see me after work but left with another girl after making plans to see me after work. We went for a group bowling session and again he was flirting with her (she told me everything) so I confronted him about it. He says I’m getting jealous over him which isn’t true I don’t like to be disrespected. I ended up having sex with him that night anyway because I just see him as someone to have sex with, “stress relief” if you like. But he’s disrespected me too much and I want to end it but I don’t know how (a lot more has happened but the story is too long as it is) x