would you befriend someone who has betrayed you?

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one of my best friends had a bf. they were together for 2 yrs and then suddenly the guy found someone else and told my friend that he has been going out with a girl. of course my friend didn't like it so she broke up with him. but the guy still communicates with my friend. they are still friends now. is it right for them to be friends eventhough the guy has betrayed my friend?