Why do some people obsessively chase someone who clearly isn’t interested?

This is something i see in men and women both. I will give an example i saw recently. My wife has a female friend who comes over occasionally for lunch on Sundays. Recently she was pretty much crying on my wife's shoulder because the man she's been chasing for nearly a decade got married and cut contact with her. He never once dated her, Never once treated her like anything other than a friend, never even did the one night stand thing. Whats worse is the "Male friends" she has, have also essentially turned their backs on her and refuse to be emotional sponges for when she needs someone to do emotional labor. This woman is in her mid thirties, and from what i know of her history, every relationship she has ever had has been a MASSIVE disaster.

I have seen men do this too but i dont have a ready example. Why do people do this to them selves?

Why do some people obsessively chase someone who clearly isn’t interested?
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