You and Nagi have been friends since childhood until they graduate, will be inseparable by anything except...

You sit in a chair far behind, you see Nagi sitting in a chair with another woman wearing a beautiful white dress, looking happy because she is 'married' to a woman she likes.

Visiting your own best friend's wedding, realizing that you have kept feelings for him for too long, so long until Nagi gets married you still don't express your feelings for him.