Millennium Darling 2006 (Boy’s Love manga)

The rumored “tsundere couple,” Sentaro Katsura and Sanshiro Sakamoto. Sakamoto’s best friend, Yoichiro Takasugi, warns him that if he keeps acting so selfish and arrogant, “Someday Katsura-kun will dump you”! But Sakamoto’s darling couldn’t possibly do that, right?