Why does this happen?

I get huge crushes on guys and fantasiZe about them but they’ve never liked me back or they ghost me etc

But the guys that actually like me and are lovely guys and I become good friends with them. I give them a shot but then I can’t fantasiZe about them or never desire sex. I sleep with them to see what it’s like but then I feel really depressed afterwards and don’t enjoy the sex

I don’t know why this happens