I believe it was a shoujo.
I can't remember to much but I believe it was composed separate stories of girls who attend the same school.
So characters from one chapter would make a cameo appearance in another.
It's all extremely vague, but any help is EXTREMELY appreciated.

1) A girl who fell in love with a guy, but they were only sex friends. She told herself that she's happy as long as she could be near him.

2) A girl who fell in love with her teacher. She said something like he has an impact on her because he fills in the spot of a father she never had (I think). She took his wedding ring, and refused to give it back unless they went on a date. I think they were on a boat and she finally convinced him to have sex with her, I think.

Thank you for your time.