a lot of people i know have been running into hard times recently with respect to love. i've been putting off thinking about the following issue so you can get my unadulterated thoughts: why does love cause so much pain? i will adopt the evolutionary viewpoint here; it's clear why love causes us so much happiness, because it's important to find a mate to pass on our genes, but it's not clear to me why it causes so much pain, enough so that many people give up on it for fear of getting hurt.
i guess one hypothesis is that because finding the right mate is so important (although from an evolutionary perspective, this is only of secondary importance to finding a mate at all), a lot of negative reinforcement is a good thing. i don't know if this question can be answered, but one thing i'd be very curious about is if love caused this much pain throughout human history; when you have a small tribe and only a few eligible people, it seems like by virtue of having limited choice the whole thing wouldn't be as dastardly.
by "human history" up there, i really mean on an evolutionary scale, like around 10,000 years ago (still a blink in terms of genetic evolution, but in terms of cultural evolution probably a good starting point.) nevertheless, it's obvious that in historical times, the pain caused by love has remained constant, or at least a constant theme of literature (romeo and juliet, medea and jason, etc.) why do we do this? the vast majority of pain here is caused by asymmetry, by unrequited love; the people that are the hardest to let go of are the people whom you love more than they love you.
one cultural solution is arranged marriages. in this situation, it becomes entirely counterproductive to be pained by love. and yet i believe it still happens; i'm not familiar enough with the culture to say that for sure, but from what little i've glimpsed and read it doesn't seem like the solution is entirely successful.
more than any other pain, the pain of a broken heart has staying power. it outlasts any sickness; this is certainly the case in celebrated examples in literature and film, but i believe also the case in real life. while i haven't been afflicted by the grim specter of death in my life, i know others who have, and the pain seems to generally go away in a time span on the order of months, not years. why? why does this stay with us forever?
the truly puzzling thing is that the behavior pattern it effects is typically not a useful one. when i have been stricken by these pangs of posthumous love, i have typically withdrawn -- become asocial, become closed off. everything i see reminds me of her; everything i do is a reminder of the pain i'm feeling, and the only way to not think about it is to cut everything off and pretend i'm not human. if pain-via-love is a meme, it seems like it wouldn't be very condusive to spreading, since its infected hosts aren't garrulous individuals.
now, i am, of course, not exactly a disinterested observer in the study of this pain. i'd like to know the answer as to why being rejected romantically causes such angst. i can't come up with why it's useful to anyone, or to the meme itself, to take the life out of a person, to suck them of social drive and maroon them on a mental island buffeted by tornadoes for a period of months or years. and maybe to cause irreversible damage, though in this case i'm oddly comforted by the fact that if it really did cause irreversible damage of this nature, it would be out of the gene pool or meme pool by now.
another possible explanation relies on the hypothesis that happiness without sadness to compare it to is impossible. that by making us feel sad when we fail, love makes us that much more happy when we succeed, and so the transcendent happiness of true love would be impossible without years of heartbreak to compare it to. that the whole thing comes part and parcel. the virtues of having love make us happy are obvious: more fidelity, more children, and it gives us something to drive for. maybe the whole thing is a trick: the sadness is there to think that if something can cause this much pain, when we do find happiness, boy will that be something, because of the power of love. and so we keep looking, only to eventually settle for the byproducts of the search. which, at that point, do make us happier. that's a more sobering thought.
anyway, my advice to my lovelorn readers? try to figure out why love causes so much pain. either you'll figure it out and feel enlightened -- and know how to attack it -- or you'll convince yourself that there can't possibly be a reason, and thus stop being sad. and on a more basic level, my advice is to realize that the object of your affection has fatal flaws, or that you have fatal flaws. but realize something; don't just reason around in circles. if the flaws are unchanging, accept them and do your best. if the flaws are changing, try to change them.
i'm not saying it will work -- it's terribly difficult to rationalize -- but as long as you keep thinking you've avoided the worst, most inexplicable part of the situation, which is just stopping.