Kataomoi wo Kojiraseteimasu.

"I'm a pro at unrequited love--I'm never going out with you!!"
Ren, a mystery novel editor, is in charge of his best friend, Takizawa, a best-selling author. In fact, he has had a crush on Takizawa, who is known as a man of many love, for 15 years! Takizawa may or may not know of Ren's feelings, but after his third divorce, he suddenly confesses to him, "I love you, be mine!" But when Ren refuses his confession, Takizawa begins to make a move on him fiercely!

(Source: Chara Comics, translated)

Note: Includes extra chapters.