Did you expect it to make sense? To be a good reason that made you go "yeah, this is totally understandable?" Can you honestly imagine that reason?So the reason for her pathological cheating was... that she got rejected once??
I'm out. I've given this more than enough of chance. Not my cup of tea
The idea of her chasing after everyone she has any attraction to because after saving up all her emotions for one guy who didn't like her back honestly makes way more sense than anything else I can think of. She's just ignoring social norms and acting deviant with a pretty understandable motive: I don't know if people will like me back the way I like them, so I can't just pin my hopes on one person. Like most people who ignore social norms, she doesn't understand why those norms exist and is sure that if nobody ever found out about what she was doing everything would be fine. Why wouldn't it be fine if they knew, though? Didn't think that hard about it.
I knew guys who chased after every girl they thought they had a chance with in high school, whether they were together with someone or 'together' or single or whatever. They left a trail of broken hearts in their wake. They didn't need some sort of sad backstory or deep traumatic event to make them do this. Why would it be any different for a girl, other than our expectations of gender performance?