Since each of us (chooses) our own friends, lovers, and spouse then that would mean each person is "getting what they want" or else they would not be there. Therefore I would say a person that ends a relationship does not do so because of "greed" but rather because there needs are not being met in the relationship.
An unhappy person that stays with you cannot make you happy. Whenever one or both people come to the realization that they do not want the same things for the relationship it makes vary little sense to waste one another's time.
In the U.S. it has been reported that (women) initiate 66% or 2/3rds of all divorces.
A divorce or breakup is nothing more than one or both people reaching the conclusion that a (mistake) was made in the partner selection process. Human beings make mistakes in all areas of their lives including selecting the wrong mates for ourselves!