In both the Buddhist way and Vedanta, the impermanence of the world experience is emphasized. True discrimination (viveka) is knowing the difference. Sri Adi ShankarAcArya says
नित्यानित्य वस्तु विवेक:
nityAnitya vastu vivekah
Discrimination (is) knowing the difference between the impermanent (Unreal) and the Eternal (Real).
The Unreal is impermanent, it is mAyA (that which is not), it is the world, which is the mind.
The fleeting sense experience of life itself and the changefulness of the mind are seen in all our relationships to objects and people in the world, perhaps most so in the relationship between a man and a woman.
Man and woman though pure of thought,
Swear undying love 'til death do us part'
If woman's words on water be writ
Man's writing on sand too lasts not a bit!
In general, women are portrayed as being fickle, but in truth fickleness is a characteristic of the mind.
So in the spirit of gender equality one must admit that man's mind can change too. In general, a woman's mind changes more often (about 12 times) because the lunar channel IdA is stronger in women (in general) than in men (in whom the solar channel piNGalA is stronger). However, there are exceptions in both men and women to this rule.
Rather than being a deeply cynical statement, this tells us that unless we have loving compassion for a person in the image of God that is truly everlasting, our relationships are liable to founder on the rocky coastline of expectation. That I believe is the true opening of the heart. In any relationship, due to changefulness of the mind there is bound to be some mismatch of expectations and disappointment. But the traditional notion of marriage being 'until death do us part' is meant to symbolize the accomplishment of seeing that image of God in one's partner consistently through all the vicissitudes of life. Of course, this succeeds if this is firm-rooted in both partners. Even if it does not, maintaining the viewpoint that the other is an image of God, however imperfect, just as one's mind is also imperfect, is very liberating and prepares the mind for genuine relationship with people and objects in the world.