Terrible memory sucks....

Home tutor is seme and Student.is the uke
Student has a crush/ in love for his home tutor and doesn't want for his tutor to stop teaching him(or at least thinks it). Student he always staring at his home tutor.
Uke will often fantasize about his home tutor or coming up with situations like being punished after messing up on questions or in sexual situations with him.
Tutor figures out uke has a crush on him

Pretty sure this was a side story / one shot in a volume

who needs drugs when you got yaoi