Guy's Behavior

He said this during our hook up , what does it mean?

3 years ago i dated this guy, I was the perfect girlfriend to him and then he f*** up the relationship by not taking it serious. Then i was just living my life & he would message me on Instagram here and there, id never reply. Then i posted myself on a date and He started going a little crazy with the dms just talking about how he needs to talk to me. He ended up telling me he loves me etc etc , And once he did that he ghosted? So i was like ok…. went back to my life. Then he came back talking about how he messed up. Anyways, now his actions seemed a bit better so he took me out a month ago, and again today. Today he kissed me and he grabbed my butt and he said “this ass used to be mine huh” and i know that was sexual but i feel like it meant a bit more. Im just asking you guys what that meant / if its relevant bc this guy does ghost me a lot and come back and show effort. I just dont get it.
He said this during our hook up , what does it mean?
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