Why do some men treat their girlfriend so badly?

my best friend has a boyfriend. she‘s really pretty, gets good grades and she‘s really nice. Quite a lot of guys have a crush on her. Her boyfriend seems really sweet and kind but she cries about him so much because he doesn‘t treat her well. He often ignores her, tells her he‘s busy and won‘t talk to her for days. He‘s not as attractive as her, doesn‘t get good grades and I think he should treat her better. why does he behave like this?

I don‘t know how to help her because she cries about him so much and tells me about it and I don‘t know what to say anymore.

Why do some men treat their girlfriend so badly?
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