いつのまにか彼女は……

The main girl has been always shy and cries easily.
The main character has been offering help to her and always in love with her.

She went to a school for girls. There again, she is not talkative and intimidated by boys other than the main character.
However, she seems to have changed recently.

He starts feeling that she is distant and avoiding him. And sometimes he sees a shadow of another man. Since when had she changed that much...?