Here's the rundown on what happened:
She was bragging to her about meeting her true love.
The 3 meet up.
Koiumu forgot something.
Mizuho ask masato to use he's guy connection to help her find her destined person(the guy that helped her).
Masato apologize cus he has no friends.
They went home.
Same station.
She meet the guy she last confess to.
He mockes her that she switch to another guy fast.
Masato protects her
He leave
She felt guilty falling for masato even though she's inlove with her destined person and koiumo is inlove with masato