Well the topic tells almost everything i remember of the manga.
It told of two guys who were in high school if i remember right and they have compete of everything since they were young.
And so in the end of the manga they compete which one can get the other one to cum first, so they compete and the black haired guy loses, but than the blond guy is still hard, so he asks the black haired guy to finish what he started, but the black haired guy refuses and than the blond starts to jack off himself, but than the black haired guy gives up and finishes the blow job he started.

And if i remember right it's oneshot.

Relationship by Kouga Youichirou?

Sekai wa minikuidesu..shika shi! Yūjō, yūki, tsuyo-sa wa ikinokoranakereba narimasen..Tiruendo!

Yes! It's that one!

Thank You Very Much!!!!