Send Them a Farewell Gift for the Lost Time (manga)

For four years, Naruse was swept up in his love for his novelist boyfriend, Toui. But tiring of his flightiness and lack of commitment, Naruse finally walks away from his relationship.

Or at least, he tries to. Every time he runs into Toui, they seem to get tangled in one another's emotions and end up sleeping together. They argue and fight, then afterwards comes the pang of regret. Maybe their relationship is doomed to fail. Or maybe, it just needs a new angle...