Why some men are so ungrateful?

Imagine a guy who had nothing, not even a roof on his end. You be with him through all, till he life gets better then he starts to treat you like shit. You break up with him because you know you deserve better. He goes to date another chick who looks glamorous i must say, but this guy who never posted me on his story, a girl he just met like weeks and he goes to post her and write one of kind.

Would that girl want her when he had nothing? Its really frustrating how you give someone your all and he just don't value you. Anyway i wanted to vent honest.
Why some men are so ungrateful?
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