What do you do when your girlfriend dumps you for another guy then wants you back?

i had a girlfriend who i dated as soon as i met her so we lasted a couple of weeks but it felt like it was months because we already started to develop feelings and we got a little serious we was already talking about having and stuff then she tells me that she wanted to get with a boy that she knew for a long time so i was like ok and she said we could be friends so then she stazrted hitting me up telling me o i mazde a mistake i shouldve stayed with you because the boy she wazsz with did not treazt her azs well azs i did so she told me that shes gonna get baq with me as soon asz she breaks up with ok so we did then like a a few months lator i found out she almost slept with my older cousin and she sent him i naked pik so i was like **** you and i blocked her aznd she kept hitting me up from different screenames what should i do ive already blocked like 10 of her screenames cus i feel stupid because my friend told me she sounds like a smut to break up with her but i disagree cus i though she was better then that but i was wrong