The title of the yaoi/bl manga that I'm looking for has a reserved/subdued storyline; no cutesy stuff or anything fluffy like that, and starts off with a student getting caught smoking on the roof by the teacher who is cool about it and doesn't scold him but invites him to eat sweets in his office instead, which becomes a regular occurrence for the two. The teacher has had a failed relationship with one of his female co-workers. This is the extent of my memory, It's been a few years, sorry!! If anyone recognizes this manga and could share the title, I'd greatly appreciate it!!! Thank you!

goodbye lilac or evergreen days?

Nope, neither of those, but I remembered something else (sorry for being so vague): both the teacher and student have light hair and the teacher has glasses. The manga art looked a little old and also never updated so I never found out which was the seme and uke. I found it on mangahere but one day my account got deleted so I lost all my bookmarks including that story.

Anyways, thank you so much for trying to help me find it!!! You didn't have to and I'm grateful for your efforts (and also for the new recommendations) ^^

(Also I don't expect you to continue trying to find it)

There was a similar question few days back and I stumble on your thread so maybe it’s one of these?
Hmm my memory isn’t very good but I remember cigarettes in these. Maybe it’s one of them.
Trap (Ootsuki miu)
Irome
Ano Kado wo Magatta Tokoro