Why did he ditch me after we spent the night together (long)?

So I met this guy (let's call him Z) about half a year ago at a party in a town very far away from my home. I was very drunk that night and ended up sitting on his lap and he lent me his hoodie because I was cold. I got too drunk eventually and was offered to sleep in a room in the dorm where the party was at. The guy which this room belonged (I'll call him G) to was supposed to sleep on the couch, but ended up in the same room as me and took advantage om me sexually.

Fast forward until a few weeks ago, I once again visited this town where Z lives, and ran into him at a bar when I went out with some friends. We didn't speak much and I instead ended up having a long conversation with a guy who was hitting on me. When we were about to head to an after-party, Z came up to me and started talking. He seemed very interested in my life and asked me a lot, but the other guy kept hanging around and Z eventually went back to talk to his friends. I wasn't interested in the other guy but he was hard to shake. I noticed Z looking for me at multiple occasions during the night, but immediately walked away when he saw the other guy was close by. When I was about to go home that night, and this guy who had been flirting with me all night was saying goodbye, I noticed Z hanging around the hallway and ignoring his friends who wanted him to come over to them. It kind of seemed like he made sure the other guy wasn't following me home?

The next evening I saw Z at the bar again. This time, my friends were eager for me to approach him, and when I didn't dare to, one of them ended up walking over to him and pursuing him to come to sit by me. He came to sit by me and we talked for a while until we left the bar with two of our friends and I ended up following him home.
27 d
We had sex but it was very brief because I wasn't quite in the mood. Instead, we talked a lot. When I briefly addressed I had a crush on him, he said "This here isn't going to be a relationship" and I laughed it off with "No, of course not!"(although I was a bit put off). He kept apologizing (both to me directly and to one of my friends) for not protecting me that night when G took advantage of me. During the night I spent at his place he revealed a lot of his insecurities and was very vulnerabl
27 d
I really felt like we connected, but I haven't heard from him then. Didn't even accept my friend request on FB. I know we live far apart, and he is 7 years older than me. But it feels weird he just ditched me after this, because he did say that he had tried to hit on me the first day and that he had gone out the other day only hoping to meet me.

Why is he acting like this?
Why did he ditch me after we spent the night together (long)?
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