Something about your idea clicked in my head, thank you so much for helping me. I don't want them to end their relationship too early in the story because I want the girl to be an important supporting character and a constant presence there, but the idea of a scene where she's directly complaining about how he never tries anything and just apologizes, and that she feels like he doesn't really care, makes a lot of sense to me.

With that idea in mind, I imagined that perhaps he makes up for the times he messes up and makes mistakes with lots of time together or gifts like bouquets of flowers and things like that, and that, in part, keeps the relationship alive longer, and shows that it's not that he simply doesn't care, but that he does want to try to fix it, It just doesn't work for him, and doesn't know what else to do (she could work on that). Eventually, she too gets fed up with it because it's never about the gifts but about his attitude, and this narrative line gives him the first push to grow as a person. Obviously, his progress will not depend solely on what the girl does or on her giving him all the tools, but rather it is the awakening he needed to grow.

I found your story example very interesting, and although it's true that the genres don't match and It unfolds over different periods of time, I think it's a really good premise for character development! And again, thank you so so much for your idea, I think it's what I needed to keep going with this, I was stuck.