Responses
I think this is one you're looking for
https://www.mangago.me/read-manga/kyoushitsu_no_yugami/
If it is, it has a prequel
https://www.mangago.me/read-manga/yugami_hajime/
so i suddenly remembered this one yaoi manga/manhwa i read a while back, but i cant find it!
So i dont remember much but its sort of a love triangle, where there is a teacher and a student who is in a sexual relationship. The student is way more into the teacher than the teacher is into the student if i remember correctly.
One day another student (who have a cruch on the student who is in a relationship with the teacher) catch them in an act or smt.
The teacher then invites him to join in.
I cant remember much more, "some of the information might be wrong since its so long since ive read it."