Have you ever felt someone was with you because of one thing only?
This may be hard to describe properly, so bare with me. Say you have a quality (the ones I think of are physical) that someone is overly attracted to, possibly bordering on fetishism. This is a large reason why that person is with you. If you desire to change that physical quality, would you worry about that person no longer being attracted to you?
Purely an Example: As a woman, you are big breasted. You are with a man who LOVES big breasts and REALLY prefers to be with a woman like that. He searches these kinds of woman out to be with and is willing to forgo other physical features as long as the woman has large breasts. So you two are together for a while, and you decide to get a breast reduction for whatever reason, eliminating the one thing he really desires in a woman. Are you afraid he will leave, lose interest, etc.?