I second Dave's comment. From and evolutionary perspective an organism; and yes that does also include us, for religiously brainwashed or any anthropocentric's :sarcastic: in this thread, and organism will move away from an entity that causes displeasure:brickwall: and toward:bigsmile: an entity that causes pleasure. The simplest action of a human hand quickly pulling away from the hot flame can be equated to how we 'naturally' go about our sociodynamics actions and respones in a relationship.

We move toward that which is pleasurable to us (the majority of the time), we move toward those that make us happy, that provide us with something, anything really, that is of some benefit to us. Self-preservation my friends, self-preservation, and many humanists may disagree but this is the fundamental driving force behind our actions in relationships. People who make us laugh, people who makes us happy, people, whose mere presence, can sometimes trigger thousands of minute neurological impulses that flood our body with dopamine and oxytocin. A mouse to the cheese, a rabbit to the carrot, for you can lead a dog round in circles, if you tempt it with a bone.

What I am getting at here is that, if these things are true, which there is an overwhelming amount of evidence for, then are we fundamentally selfish beings? Self-preservation is ultimately a selfish drive. Think of your last partner, can you honestly say that you would leave them forever, if you new that there was someone out there who could treat them better? Love them better? I doubt it, we are too hung up on our own emotional high to ever relinquish something so euphoric. In the intermediate phases of the initial infatuation and most likely from that point onwards, we are obessed with these feelings. I recently asked a lesbian friend of mine, why she was so interested in a girl she had just started dating? I got the typical response that I expected "because she makes me feel good". Emphasis on the 'me' part. Is it wrong? to be selfish? shouldn't love, or rather, the most pure form of love, be about wanting the best for the other person, wanting to please them and make them happy? We are selfish, we do not have to be, but we are, naturally, either embrace it or try to change it.