So I remembered a shoujo (or is it josei?) manga. And I tried to remember or search for it, and I couldn't find it. But I still remember how the story went so here is how it goes (might not be accurate):

A girl who is a senior (in a university?) was dedicated to get into a relationship with a guy. She remembered the time before when she was a junior, and she was very cute, so a lot of guys asked her out but she firmly rejects everyone because it was something about JuniorsxSenior aren't allowed. (she really regrets it lol)
Back to the present, a guy asked her to turn around, and when she did, the guy took a picture of her because her panties (im not actually sure if this happened? or is this scene from a different manga lol) was showing. The guy used it as blackmail to meet her in some place.

...Blah blah blah....The guy, which the main girl thought was a student, turned out to be a sensei (or professor) in her university (?), and found out that the guy was actually one of those seniors who tried to ask her out.
...And they lived happily ever after. lol

If someone really did find out what the title of this manga is, i'm amaze

Third story 1/3 no Kareshi of Suki ni Naru Made Matte...

Be amazed 😁

~4400 manga completed
~1700 ongoing...

omg thank you very much. i am literally amazed 😲 😲
Hats off to you~