I've noticed that kind of plot is used a lot for side characters like in Soredemo Sekai wa Utsukushii. Bard was in love with Livi's mother, Sheila. Even though she couldn't return his feelings, it seems like she intentionally was very close to him to make up for it.

Well are there any where that's the case for the male mc? He's in love with his friend's/brother's significant other. He's close to that person (the girl) though as well. In the end, she realizes she loves the male mc instead and they get together.

I'll also take instances where the girl the male mc is in love with, might not be the friend's/brother's significant other, but she's in love with him. In the end though, she realizes her love for the male mc like in Toradora.