I'm not going to bother about my brothers girlfriend cheating with someone he knows
Why wouldn't you bother with her cheating behavior?
She did the right thing. My stupid brother did not deserve her
It's your brother so you should be telling him about his cheating girlfriend if you know about it. If your own family doesn't have your back, then are you really their family?
Family isn't everything you know? He hasn't been that great to me.
He might not be that good of a brother but he does not deserve to be betrayed by the person he loves and by family. He might cut you out of his life when he finds out that you kept it from him.