I thought this article was interesting. The writer is a bit flowery, so it's not strictly science, but it's science-y. It basically says that your brain is constantly rewiring based on its daily experiences and romantic relationships have a strong impact on that process.

Your initial imprinting occurs as an infant. No surprise there. We've heard this for years now. The author states that the initial imprinting from an infant's primary caregiver (read "Mother") affects later choices in romantic love.

Thanks to advances in neuroimaging, we now have evidence that a baby's first attachments imprint its brain. The patterns of a lifetime's behaviors, thoughts, self-regard and choice of sweethearts all begin in this crucible. ... It's not that caregiving changes genes; it influences how the genes express themselves as the child grows.

That last part sounds similar to epigenetics (which is awesome, btw), where gene expression is caused by a trigger rather than a change in your DNA.

So, hopefully, whoever took care of you when you were an infant did things right, otherwise you might be screwed when it comes to your relationships, which in turn screws up just about everything else.

"Scientific studies of longevity, medical and mental health, happiness and even wisdom," Dr. Siegel says, "point to supportive relationships as the most robust predictor of these positive attributes in our lives across the life span."

The supportive part is crucial. Loving relationships alter the brain the most significantly.

...
James Coan, a neuroscientist at the University of Virginia, conducted experiments in 2006 in which he gave an electric shock to the ankles of women in happy, committed relationships. Tests registered their anxiety before, and pain level during, the shocks.

Then they were shocked again, this time holding their loving partner's hand. The same level of electricity produced a significantly lower neural response throughout the brain. In troubled relationships, this protective effect didn't occur. If you're in a healthy relationship, holding your partner's hand is enough to subdue your blood pressure, ease your response to stress, improve your health and soften physical pain. We alter one another's physiology and neural functions.

That's right. Having the right partner gives you a +1 on your saves against electricity damage. Having the wrong partner is like putting on a cursed ring. (That's right. I just used a D&D analogy cause i'm a big geek. But you totally understood it, so you're an even bigger geek. So there.)

This is prolly the best line in the whole article:

Staring at a picture of a spouse lit up their reward centers as expected; the same happened with those newly in love (and also with cocaine users) (emphasis mine).

Woo! I love a good cocaine reference!