Why have sex with someone you don't want to be with?

So this isn't about me, it's about a guy and girl that I know. Anyways my friend (the girl) has this huge crush on a guy and has been wanting to date him for some years now. He constantly told her he didn't want to date her because he wasn't all that attracted to her. They weren't having sex atp. But she stuck around anyway and would refer to herself jokingly as "his bottom bitch".

A few years passed and he went through a breakup with another girl and it was pretty bad. So anyway he started having sex with my friend, even tho he didn't want to date her and knew she wanted to date him. And they would do things like go to movies, get dinner, spend a lot of time together, etc. Long story short my friend freaked out and went off on him about not dating her, so he blocked her number.

I guess I just want opinions on who you think is in the wrong here? The guy for sleeping with someone he knew he didn't want? Or my friend for sleeping with someone who she wanted to date?

Again I'm a third party in all this.
Why have sex with someone you don't want to be with?
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