Dear Green: Hitomi no Ounowa
Eight years ago, Yajima and Outomi met in high school, through Ryouko, Yajima's best female friend and Outomi's girlfriend at the time. Ryouko remained in their home town, but Yajima and Outomi moved to Tokyo and remained close friends through university, and after Yajima dropped out. Yajima feels comfortable with Outomi -- unlike with his girlfriend. Then one day Outomi kisses another guy just to see what it would feel like, and Yajima gets agitated beyond what seems reasonable for even a close friendship.
Volume 1: xx Happier
Volume 2: Stalking Baby, The Direction of Desire (The Direction of Longing)