Sadhguru
Why did my relationship turn bitter and end after the excitement faded?
Relationships built on extracting happiness
If a relationship is body-based, the excitement about each other's body usually dies after some time. Such a relationship is about extracting happiness from another person, and when it stops yielding what it did in the beginning, some bitterness begins.
If you try to squeeze joy out of somebody, then after some time it stops yielding what it used to in the beginning, and bitterness begins.