One nail drives out another

A bittersweet love triangle between a mysterious, kind man who offers his physical conffort, and his childhood friend.

Tira is being teased by the unexpressive and unsociable preeschool teacher named Kaji whenever he goes to pick up his nephew.
Prequel: Ookami Papa wa Hitsuji Tsura shite Yatte kuru.

After Kashiwagi Ayumu's unrequited feelings towards his best friend were discovered by his club senpai, Sawatari Atsushi, he is blackmailed and forced by him.
Precuel: Self Portrait

After a very long unrequited love Toshiyuki decides to give up on his childhood friend. Then Jun who has always supported Toshiyuki's dejections, offers himself as a lover.

Masami and Ryuuji called a truce in order to not attack their friend Shirou, and so they'd mutually release physical necessities to endure.

Kouki has had feelings towards Katakawa, his caretaker and sensei at the family's Kendo dojo, but he in the past had feelings for his older brother.
Precuel: Scandalous Seiryo University
Related:Still...

After have had a trauma and being spreaded with rumors at his school, Endou Hiroshi started to work at a convenience store where he meets the cold and arrogant Yamai Kouhei

The main couples start with a platonic/unrequited/impossible love;
Junjou romantica, egoista, and terrorista, even Kaoruko Usami's story, and as it's well known the plot, I don't have more to add.
Related: Sekaiichi Hatsukoi
Junjou mistake

Ch 2: After found his fiancee cheating on him, being beated until be hospitalised and lost his job, Tadano wandered around until the train station thinking if it's worth to live, then a stranger guy suddenly started to talk to him.

After being blind for 10 years, Kai recovers his vision through a corneal transplant. But why can't he leave his sight of Doctor Hizuki? who performed his surgery, and why he has a weird sensation towards Hizuki's fragrance?