Ore o Mite.

When they were kids, Kyousuke always thought Saku, his childhood friend, was a girl, and when he realized Saku was a boy he was already in love. Even though Kyousuke held back because he thought having a boy like him would be an annoyance for Saku, one day, he saw kiss marks all over Saku's back... The wholehearted complicated days of love between childhood friends.