The female protagonist used to date this guy back in highschool, but they broke up because she wasn't ready for a relationship. Flashforward and she's now in college and they meet again. Later on they find out their neighbours.
http://www.mangago.me/read-manga/why_did_you_come_to_my_home/?av=2
is it perhaps this one?
The manga in question was a collection of multiple standalone stories. I can't remember if there were any explicit scenes, but I do know that the chapter I'm looking for didn't have any.
One of the guys had black hair and the other had a lighter color hair. The latter of the two was an idol, so he was often absent from school. There wasn't much interaction between the two, in fact there were only two scenes. Back when they first met and their last day of school. They don't meet after that. The story ends with black haired boy in college talking to a classmate about idol boy.