What should I do?

My (EX) Girlfriend broke up with me because me and another girl were flirting/"sexing" and i understand the reason she broke up with me, it was completely logical. We had a long fight and now she is on vacation, she will return in one week and says that maybe we could be together again but i don't think it's a good idea because i'm an asshole and something like the thing i did will probably happen again and i don't want to "Hurt" her again. (Now i do understand that i'm only 15 and a lot of Girls will Come and go but please answer on what should i do with this topic)
What should I do?
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