Argument between friends..who is right?

The way you present it, the guy is the most wrong because he chose to attack the girl after she tried to be nice about breaking up. His reaction basically is over the top and indicates that he really liked her and is now hurt and trying to get even with her by bad mouthing her. This is childish and undignified. The girl then attacks back which is lowering herself to his level, which she should not have done. Thus, in the end, they were both wrong. However, I think the boy is more wrong since he was the first offender.