KIZUNA

From childhood friends (since elementary) to lovers (since high school), Kei and Ranmaru have been through a long road consisting of hardships and fond memories. Now in college, they face a new challenge to their relationship when the son of a Yakuza boss (and incidentally Kei's half-brother), Kai, attempts to steal Ranmaru from Kei (and, of course, fails).

Synopsis from Anime News Network