It's a yaoi (or Shonen ai, I can't remember if it got graphic) about an older uke and younger seme. The seme saves the uke from being falsely accused as a groper, they somehow end up getting together (once more, I can't remember how) and it's eventually revealed that the uke is an ex-student of the seme who always had a thing for him.

Only You (MOEGI Yuu)
Only One (MOEGI Yuu)