Well, yes, the “I was nice to you why aren’t you sexing with me?” trope is very bad.
The two I remember specifically were people I legitimately liked. One of them we spent like hours talking after class a couple times. But when I asked her out for dinner she replied she had to help her boyfriend study.
I can see her perspective of just having a friend to hang out with, and then being annoyed when the guy wants to make it more.
But I am legitimately confused how to square what you’re writing about with the advice of “ask people out you know in real life” some people give. That was the advice I was getting back then. Meet people. Be friends. Ask them out.
Now I use apps so I know the other person is in fact available to date, and does date men. Also I’m old and my relationships currently are fine.