Hey Teach... I'll Make You Feel Good summary:

I'll shove it all the way in this time around." Saeki is a university professor who has just found out that his boyfriend of two years was cheating on him with a woman. At a bar, Saeki gets incredibly drunk, confuses the person sitting next to him for his ex, and ends up getting nasty with him in the restroom.The next day, a student comes up to Saeki after class. It turns out to be the guy from the bar! His name is Yamamoto, and he apparently came to pick up where they left off...! This is a story between a cute, puppy-like student who can get a little rough and a university professor who likes it that way