If you waste few brains cells in this matter, you'll understand at some point, a relationship between two beings as a state of mutual understand. more specifically, both parties generate a neutral venue or a comfort zone to live. In here, both need the good human qualities like patience, understandability, flexibility, adaptability and so on. Both have to sacrifice some things in order to build a good relationship. In here the concept like living together can be practical than arranged marriages. In a living relationship, both individuals can easily work together to build a common ground. If this process is not gonna work, the legally unbound couple can be move on easily than married.
However I don't think that a romantic relationship is a must-have element in life. Some people live happily without one. But I believe everyone needs a passion based on love to live a better life. That's the compassion or the discovery of yourself. According to Buddhist perspective, compassion comes when you discover you lose yourself in some way. through art, through understanding, through knowledge, knowing that you have no boundary, knowing your interconnectedness with other humans. According to Bob Thruman, a budhist scholar (http://www.ted.com/talks/lang/eng/bob_thurman_says_we_can_be_buddhas.html) when we are relieved from the I, me, my, mine (selfishness) chain of life, we feels ourselves differently.