I definitely agree that self-esteem plays an integral role in any relationship, although, contrary to what many people believe, I don't believe one must love oneself before one loves another. My wife and I both fell in love with each other before we fell in love with ourselves, and to be honest, we're still working on the second one.
I would say that throughout my life my self-esteem has wavered. There are periods of my life when my self-esteem was soaring and other periods where it was dwindling. It depends on circumstances, personal successes and failures, and how I judge myself.
This is the way I see it. Poor self-esteem affects relationships because poor self-esteem and high self-esteem have different frequencies. When we are resonating at one level, we're not resonating at the other. So if we have a shift in our own self-esteem, we emit different "frequencies" and begin to attract and repel different people. This in turn reflects our relationships since the people we relate to resonate at the same frequency as us.