Yaoi title?

I'm looking for a yaoi manga title that I've read a long time ago, where the seme is a writer/novelist and his lover is a student (in high school, I think). They are the MCs for this work, but I'm not really interested in them. I'm really after the second couple in this manga, which is the writer's colleague and the student's classmate/bestfriend.

At first, it was the colleague who was the seme but eventually, he became the uke while the classmate/bestfriend became the eventual seme. The colleague initially had a thing for the main couple's uke and he even tried to rape him, but failed. The classmate/bestfriend is the cool, quiet type, who is the son of a high-ranking yakuza. Their family has various clubs in the red light district. The yakuza group I think also appeared in another work of the mangaka.

There's a third couple in this series, but can't remember any detail about them.

Thanks in advance!