I'm looking for a fairly recent manga where it's the first day of high school for a high school student who actually stumbles on his home room teacher (uke) and another teacher (PE teacher?) or student having sex in the teacher's room. He was lost or late for the school opening ceremony. He just sees them from the window. (The window had curtains half open) He acts like nothing happened.
Later, he sees the home room teacher again and just locks eyes with him.
I didn't read more so I don't know who the seme/uke/ pair was but I do remember the manga starts with the other teacher asking the uke teacher to do it before the school ceremony because he was horny.

Thank you.
I read it on MRM . I may have gotten some details wrong.

Bumping!