A couple of years ago, I came across a TED talk. The presenter detailed that modern marriages are romantically dead. There is now a genre of books written to address women who want to rekindle their marriages. But I think it tells something deeper. It is not sex that makes a marriage meaningful. It is the vows. Sex is as meaningless as any other source of pleasure, like eating Pizza. It satisfies your palettes temporarily but gives you no long term satisfaction. Soon, you need Pizza again. This desire keeps you enslaved. Those who want to find happiness this way are hamsters on a wheel. They'll never be fulfilled. Slavery an joy don't go together. Think of the best friendship you have had. Was it based on materialistic gains or truth and honesty? Chances are the latter is true. It was the implicit vows of friendship that made it meaningful. Think of any meaningful relationship you have ever had, with a sibling, relative, friend, or even with an animal? Was it because of superficial reasons? Was it because there was physical pleasure involved in it? If you honestly examine your past, it may occur to you that all your meaningful relationships stemmed from virtues or values, not from superficial things like money and beauty. The same principle applies to marriage, too. It is not romance that brings meaning or satisfaction to relationships. It is the vows of marriage or of a romantic relationship that enriches it with meaning and depth. If the vows are not kept, no amount of sex can bring meaning to it. The truth is those who say they are no longer interested in their partners were never interested, to begin with. It was just a phase and they were trying to found a marriage on it on something temporary. If a man marries a woman for her beauty, he's destined to be unsatisfied, for beauty is ephemeral. Even Ms. Universe will age. Her beauty will fade. The same applies to a woman who marries a man for his money. She, too, is destined to be unsatisfied, for she will meet men who are wealthier than her husband. He may also face financial problems occasionally. At that point, her marriage would destabilize. It had no real foundation, to stat with. This is why virtue is necessary. Virtue is needed for both partners to keep their marital vows. Thus, a marriage must be premised on virtue, when both partners have proven themselves to be truthful, honest, and loyal. Unlike physical beauty, virtue grows with time, so a marriage founded on virtue will only get more and more meaningful over time. Superficial foundations, however, only lead to superficial relationships. If your relationship is superficial and full of insecurity, superficial things were exactly what you looked for.
The principle remains consistent across all relationships. There are implicit and explicit vows of every relationship. Only when they are kept do relationships have any meaning at all. Otherwise, people are doomed to continue living the life they are living right now.