I Want to Say She's My Girlfriend, but I Can't

“I promise no one will ever find out, so don’t break up with me—!” Koharu finally becomes a couple with her childhood friend Yuzuki. But his club strictly forbids romance, forcing them to keep their relationship a secret. At school, she can only watch as other girls approach him— even though she’s the one who’s actually his girlfriend. A secret love story between childhood friends, filled with sweetness, jealousy, and hidden affection.

https://www.cmoa.jp/title/353524/