Jibun Katte.

Whenever Tomo gets a girlfriend, his selfish childhood friend Hideaki comes between them. Now that Tomo has a new girlfriend, he's on the lookout, but nothing happens. Thinking the lack of intervention strange, Tomo then discovers that Hideaki has a new lover—a man! Maybe he was just showing off, but Tomo can't forget how gentle his friend looked when he was worrying about love.

A straight guy easily moved by kindness and affection and an egotistical hottie with a strong desire to monopolize. They can't go back to the time when they thought they knew everything—a romance blossoms between friends.

(Source: Shinmakoku Scanlations)