Is it related to sleeping pill or smt? http://www.mangago.me/read-manga/kawaii_senpai_no_kaigoroshikata/
Maybe this? Ik I've read another similar manga so I'll see if I can find it.
http://www.mangago.me/read-manga/kimi_no_shiranai_xx/
no, that's not the one...!!! (︶︿︶) i think they are university students.
Here's the other one! It matches your description almost completely except for the seme part and maybe a few tiny things. Sorry if im not of much help.
http://www.mangago.me/read-manga/yume_yume_okirukoto_nakare/
that is the one (๑•ㅂ•)و✧....!!! thank you MY HERO...!!!! (づ￣ ³￣)づ
im looking for a manga where there are two friends, i think they're best friends, and every day the uke gets drunk and the seme fucked him ლ(´ڡ`ლ) and the uke never remenbers... i also know it is very smut...!!!