Our Everlasting Vol. 2 (manga)

Surfer dude Houryu and shy intellectual Shouin are very much in love. Their days together are filled with happiness, but when Shouin's French tutor, a handsome and openly gay man named Nanami, makes his affection for Shouin known, doubts begin to surface between the couple. Houryu begins to suspect the relationship between Shouin and Nanami, while Shouin begins to believe Nanami's theory that Houryu is at heart a straight man and will turn to a woman when his experimentation period with Shouin is over.