What are some reasons guys want their girls back even after the guy was the one to break things off?

I'm starting on a novel about a love story (original I know haha) and I have the basic plot line and characters figured out. In the story, Sasha and Maxine first meet in a chemistry class. Sasha's older sister is best friends with Maxine's older sister but Sasha and Maxine have never actually talked to each other. But then, Maxine catches Sasha's eye just before the end of the school year. She's wary of starting a relationship because she's going to college in another state come fall but Sasha is still in High school, but he manages to change her mind, and they start an amazing relationship. Then Maxine decides to transfer to a school in her home state, but only a few months after returning, Sasha suddenly doesn't want a relationship with her anymore (not because of infidelity or anything like that--he just suddenly changes). Maxine begs and pleads for him back because she never expected to fall so deeply in love with somebody only for them to suddenly change their mind. In my story, I'm planning to go into detail about their time apart and how it is for both of them, but eventually have Sasha change his mind about breaking up with Maxine and want her back. My only problem is, since I'm a girl, I don't know the kinds of things that would make a guy want the girl he broke up with back. I know stuff like this happens, I just don't know why. As a girl, it's hard to imagine why a guy would want someone back if he dumped her in the first place. Does anyone have realistic instances of this happening and why it did or does happen? I want this story to be as believable as possible and not have to write it guessing whether I'm correctly thinking like a guy. Thanks in advance!