I think that we're at an extreme end of what started out to be some positive thinking, like: "women can actually survive on their own and don't need to be dependent on a man", "divorce isn't the end of the world", etc. And then that movie... was it Basic Instinct? The one with Glenn Close as a pathologically obsessed woman in love... and celebrity stalkers and such, and the concept of [i]needing[/i] a partner took on the connotation of mental imbalance. Now, I think, we have all sorts of conflicting messages of what single life should be and what married life should be that it's difficult for anyone to be happy, in or out of a relationship.
As wildcat says so eloquently (I really love your humour, wildcat!), humans are social beings and of course we need love and caring in our lives. Perhaps the problem arises when "need" crosses over to "needy". I'm a giver -- it makes me feel good to help other people. Not to the point where they are dependent on me, but rather in a "hand-up" sort of way. I've learned that, particularly in a state of low self-esteem, I have to be wary of that crossover point or else my energy gets totally sapped. I've been in 3 serious relationships since my divorce 8 years ago, and in each of them I somehow evolved into the one who was emotionally supporting the other. (Hey, I'm the one with MDD here -- how does this happen?) So the happy-with-yourself-before-happy-with-another bit is really a good idea for me, and I've decided to steer clear of men while I figure out how to define that boundary more clearly.
I have a amazing and beautiful friend who is so utterly miserable when she doesn't have a man in her life that I really wish for her the ability to be happy with herself as she is. That goes to Danielle's point about not placing all your happiness in someone else's hands.
I've seen relationships where there is so much love and need on both sides that I think either one would shrivel and die if the other one were gone, with no pathological element like Glenn Close or my ex-husband. That seems to me to be perfectly healthy and rather wonderful, actually.