Hello! I would very much appreciate it if someone could help me remember the title of a shoujo manga with, from what I recall, this type of premise:

The heroine goes to live with her father and enters a new high school. Sounds typical, right? However, she meets two boys who seem to get along immensely! The heroine seems to become more attracted to the dark-haired boy, while bickering more often with the lighter-haired boy. At the school, she befriends this girl who, I think, has or had a crush on the lighter-haired boy, but it was pretty much a ruse. Erm...oh! The dark-haired boy has a thing for the lighter-haired boy's older sister, who teaches at the school. I think she teaches choir or something music-related. Also, the girl's father seems to have something going on with the dark-haired boy's mother...? And at the end of each chapter, there's a letter from the heroine's.

That's all I can remember right now, sorry!

OUJI TO HERO seems to be what your looking for

Principal
Seems like

Oh, yes, it was Principal! Thank you guys so much!