It’s okay to break a few hearts
I once knew this total womanizing maniac (TWM) who defended his actions by saying something to the effect of, "At least I go for the things I want, when I want them."
Having been wanted and then unwanted, and having had wants that eventually died out, I now know it's unfair to assume that TWMs begin relationships with the end on the forefront of their minds. Most people aren't that sadistic, and probability and intention are two very different things.
In any case, while being greedy is never a good idea, I think it's smart to give your wants (all kinds, not just people) room to shift and change. Maybe they won't alter too much, but probably they will over the course of your life, and if you can't take yourself away from them for just a minute it's likely that one day you'll wake up and wonder why you've been trying so hard for something so dull.