I read the koisuru boukun and it wasn't like this manga....(づ ̄ ³ ̄)づ
We don't see them again after this. Masaki forced himself on Kunihiro the first time so you can't really go by that to know if they will switch again in the future. Masaki seemed to be the bottom for Morinaga back in the day, Kunihiro tops him here...so he's usually a bottom, I'd say (by yaoi rules - not real-life).
I want him to marry the blond girl ヾ(☆▽☆)
So she and medi could be a family and everyone be happy