Relationships can get really complicated, really fast. One moment everything seems to be smooth sailing. The next moment we've hit the doldrums and are navigating gale-force winds and 12-foot waves! This is especially true when there is an element of physical intimacy in a relationship. The swings can happen much faster and hit bigger extremes in this stage.
The trouble is that too often, our idea of love is closely tied to the body. This is, I think, a very stunted definition of love. To limit the experience of love to just physical would be to limit the possibilities that it offers. Love can be a powerful transformative tool to reshape and take our lives to an altogether new experience. If we can move past the physical aspects, and make the experience of love a means for spiritual growth, altogether new avenues open up in our lives.
Even the famed "textbook" on sexuality and love-making, the Kamasutra looks at love as something more than just physical intimacy. Contrary to popular belief, the Kamasutra is not just about having better sex. It also includes several sections on making marital relations better, and how both man and woman can take their relationship beyond just physical intimacy.
There is nothing wrong with physical intimacy, and it can also play an important role in building healthy relationships. However, to limit a relationship to just the act of physical love would be to miss out on too many opportunities to truly include another life into our own. Only when we can make another person a part of ourselves on a level other than just the physical, can we make a relationship successful. Indeed, leading a joyous, blissful life is only possible if we can include those around us into ourselves. Including everyone into ourselves physically is naturally impossible. It is only by looking at an aspect beyond the physical body that any possibility of universal inclusion opens up.
The physical act of sex has its purpose to serve in the scheme set forth by Mother Nature. Considering the burgeoning human population and the explosive growth we've seen in human numbers in the last century, I'd say we've wholeheartedly and even over-enthusiastically fulfilled that particular scheme. So I think we can afford to take our relationships beyond procreation and see how we can set them up as tools to transform our experience of life.
This is not to say that many of us aren't already doing that. But I believe we are not doing this as a society, and as a species as a whole. Every other piece of Mother Nature's creation has no such option. They are driven by instinct. But human beings hold the potential to look beyond instinct. If we can collectively shift our idea of relationships from being a tool for the survival of the species to a tool for the transformation of the species, it would solve a whole lot of problems the world is facing today.