Hey there, there's a lot of yaoi that fit that description but one that comes to mind for me is this one
http://www.mangago.zone/read-manga/oreshika_shiranai_karada/
If thats not the one you're looking for I'll try to find another
all i can think of is: http://www.mangago.zone/read-manga/bukiyou_na_silent/
Both were not it, but the first one was close, similar story. I would add that the seme is straight to begin with and I think it’s one shot (?)
Help me pls!
All I remember was they were classmates and uke confesses to seme; seme was curious so he accepted. All I know is that later on the seme was head over heels for the uke, even thinking that he wouldn’t have thought sucking a dude. I’ve been looking for it everywhere but the name won’t pop up ;-;