They are brothers and sisters who are not related by blood.
She has always loved her "brother" deeply
He has always loved his sister,
Until one day, he discovered that his love for her was not just as simple as his sister.
Until one day, she felt that her love for him had become so tired that she could no longer watch him linger in the tender homes of other women.
Until she chose to leave and give up,
Only then did he realize that he had always loved her not as a sister, but as a woman.