Seme obsessed with butts?

So some time ago, i read this manga where the seme was obsessed with butts, and lost a lot of relationship because of that. And then he noticed that his bestfriend had a good ass, and he asked him if he could touch it, and then i don't remember if they went all the way, but they did some. Then some things happened, and he found out that the reason he was so obsessed with butts was because he saw his best friends butt when they were younger.. Does anyone know the name of this manga?