Bitter Sweetness

Doctor x maestro. A doctor accidentally hit a kid with his car and when he brought the kid to his clinic, it turned out his father is a famous maestro, whose peculiarity piqued the doctor's interest. A few years later, the doctor, having lost his wife and son in an accident, happened to see the kid he saved years back and also meet the father, who is actually much more complicated and messed up than he thought.

A yakuza named Hikaru Fukami happened to hear the play of a second-rate pianist and took a liking to it. He asked the pianist to come to teach him piano and after some time, the pianist who is gay, fell in love with Fukami, knowing full well that Fukami was a dangerous guy and that the guy had a few screw loose.

He happened to catch the class' popular guy jerking himself in high school and had been in love with him since. Now they were salarymen from two companies who work together in a project. But the guy was straight. He even thought of proposing to his girlfriend despite the woman "not being the one" for him.

That guy mumbled an "I love you" on their graduation day. Years later, they met again and he thought he could finally respond to his feelings, but it turned out they were too late...far too late.

Yakuza x doctor
"You are mine, but I am not yours," was what the yakuza said when he realized the doctor's feelings for him. He came uninvited, but never came when he was needed. He kept testing his feelings by saying he had found another person to have sex with so he didnt need him anymore and yet he kept coming back.

Shounen ai.
The first person he ever loved was in an unrequited love with their professore. But maybe it was not unrequited, after all. He had to choose whether to broke them off or to let the person he loved go.

Step brothers
He became a recluse when his younger step brother found him sucking another guy's dick and told the whole school of him being gay. What was worse, though, was the fact he could not come to hate his younger brother. No, instead, he loved him.

He was the one who opened up Ken's heart when he first transferred in middle school. Now they were third year in high school and they would have to part ways. He was worried of leaving Ken alone. But whom exactly couldn't be left alone? Ken...or himself?

Masterpiece! Highly recommended!
One was a boy whom his father prostituted since he was a child. The other was an assassin trained to be a killing machine without name or emotions. Two people from the dark world met and felt like they completed each other.

Bitter without sweetness. When he chooses the arranged marriage over the one he truly loves, a broken heart is all he'd get.