Not quite sure but my assumption that the only reason the male and female protagonists grew apart is that I'm pretty sure female idols aren't supposed to have relationships. Plus with the male mc going away to a college in Tokyo, I assume the male mc couldn't keep things up for logistic reasons.
is it just me, or does it seem like this is gonna be a your lie in april-ish kinda thing where male mc and female mc will regain their passion, the male mc goes through the surgery, and ultimately ends up dying in a failure or something, but still lives on through music or some random thing