I really love one thing in manga. English isn't my native language so I'll explain in easy words.
A main hero is a nice, intelligent boy sometimes even a class president. In his school/place he works there is a guy who makes love to many boys in many places. When a main hero see him having sex it's just a coincidence but later he is peeping and again. In the end he sleeps with this guy himself.
Hope I explained it in a good way.
A situation like that takes place in oneshot Sukima (it's chapter 4 in manga Omoisugoshi mo Koi no Uchi).
Hope you can help me with finding others yaoi like that. I'm sure there are many of them but I can't find. 😢

maybe in some way Cold - Zettaireido no Koibitotachi, Dekiai Rule, Himegimi wa Ore no Mono- 1) The Princess is Mine

I have the simplest tastes. I am always satisfied with the best.

• Oscar Wilde -

Thank you for answering. But it's not really the thing I'm looking for.
It must a boy (innocence one) who doesn't think about sex until he see a guy doing it with some other guy.
There is not even that kind of category. 😔
Don't know WHERE and even HOW should I look for it. 🙁

There is also other think I'm looking for. It happens in Martini Kouryakuhou by Tateno Makoto. I mean, in high school we have a couple of two young boys. Older one decides to break up and wishes his boyfriend will find in the future a girlfriend. After couple years he meets him again and realizes he is a very good looking man now and he still has a feeling for him. But he really did had found a girlfriend.