I think some of us, myself included, are just so intent to remain who we are, or to pursue who we want to be, that we end up preempting any chance for long term love or commitment.

As you allude to, it is a sort of selfishness. However, I think it is far more selfish to commit to another when our first, true priority is ourselves. So, with that in mind, I think we are unselfish in that regard. We'd like the stability, warmth, and satisfaction of a long term relationship. We're just not willing to pay for it. And we know it.