I think this is a tough question,because if you are a boy you will probably say that girl is more often to break than a boy and vice versa.
Well for me i could say boys is more often breaks the hearts of a girl,because man is more weak than girls.
Yeah in a teenager,if they don't like the guy that courting her maybe that is the reason.but sometimes there is a reason why she breaks that guy maybe she saw that boy is flirting with other girls.
well for me it's equal, there are girls who is unfaithful, weak, unsatisfied to their partner just like some boys do. we cannot say that only boys is more often in doing that thing because now a days girls are like boys already.