Sorry, but that's what happens.
Lot of twists and turns at the end there.
Maa-kun isn't the same Maa-kun Yuki fell in love with.
It turns out the love rival was a real tomboy in her youth, and that's the Maa-kun Yuki idolizes and loves so much.
The love rival that is competing with Yuki for Maa-kun also fell in love with the wrong person. She was saved from a molestor by a guy in a Hawaiian t-shirt, the sort of t-shirt Maa-kun likes to wear.
After this is all revealed to everyone, Yuki encourages Maa-kun to get together with the love rival.
Yuki gives up on pursuing a relationship.