Well, seeing as no one has brought it up yet, I will give the evolutionary account of love, and then after that I will formulate what I believe to be my account of cultural/sociological love
Evolutionary Account
a] A brief account of socialization and its place in human evolution
Love, in its most fundamental and basic constituency is evolutionary. There is no running away from this fact. Human beings evolved over an extremely long period of time from simpler organisms through the process of natural selection, which ultimately "chooses" the most fit constituency of genetic disposition in a particular environment that serves as a means to reproduce and survive. Humans are an extremely complex organism, who has evolved brains that can conceptualize and socialize, in combination with a wide array of other functional tasks. In fact, this socialization was a huge aspect of our evolutionary history which developed out of our environment of evolutionary adaptation. What purpose does socialization serve? Well with out going into too much detail, (because there are literally whole text books written on social evolution) socialization serves as a means for group solidarity, which in itself is very adaptive. It allows for groups or bands of human beings to live together harmoniously and synergistically, which serves as an adaptive means for accumulation and garnering of resources (food and sex) - and ultimately increasing chances of survival exponentially so. If human beings never evolved the ability to socialize and develop social ties, we simply would not have evolved to where we are now. It is one of the most fundamental aspects of our evolution. Just think of the advantages a group of humans has in a harsh environment (predators, scarcity of resources) over 1 human, fending for himself. A group can consolidate resources with each other, and help rear offspring, with an overall more efficient means of protection for in-groups. Anyways, I will leave it at that in terms of socialization just to show you, with some evidence that socialization is in fact an evolutionary product.
b] Love as an aspect of socialization
This leads me to an ASPECT of socialization which is the topic of discussion here: LOVE. Love is a fundamental component of socialization that derives form evolutionary mechanisms. There are different levels of love and the ways in which our genetics predispose us to love, which ultimately serve different functions. Our genetics make it so that we FEEL as though love is a real emotion, that derives from some higher form of metaphysical realm. Evolution, via natural selection, has worked in a magnificent way to make it so that we think and feel that love is MORE than an evolutionary trick to propagate our genetics. This is why love is such a strong emotional bond, and why it affects us so deeply - merely because it has been written in our genetics for hundreds of thousands of years. Love is something that we can not simply "give up" if it isn't serving our interests emotionally - this is because evolution "knows" what it means if we are invested in a love bond - namely as a function for offspring rearing and production. This is why when we break up with a girl or vice versa it is EXTREMELY emotionally draining and hard. We cant simply go no contact without some turmoil. We want to know what they are doing, we want to talk to them, hold them, profess our undying love for them, look them in the eyes, touch their obscure birth mark, smell them. Its an evolutionary trick. A combination of neurological processes and hormonal mechanisms working together. Love more often than not comes with the simultaneous engagement in sex. Why do you think that is? That love and reproduction are so synonymous? This clearly shows that love and sex go hand in hand. When humans have sex there is a chance of pregnancy, which is the evolutionary imperative (propagating genetics) and thats why you grow this emotional bond towards that person because it is more adaptive for genetic propagation to stick around (through the strong emotions of love) in order to give your offspring the best chances of survival. This is also why hormones are released throughout the body when two people engage in sexual intercourse. These hormones are the starting blocks of love, and eventuate in to full blown "in love" - an evolutionary function. Evolution is a complex mechanism that is very good at what it does - which is making sure organisms spread their genetics. It will produce traits in organisms that make production of offspring more efficient. Love is one of the most efficient evolutionary functions ever produced. So much so that people have ascribed love as being derivative from an ephemeral metaphysical teleology - not a physical byproduct of our neurology. I think that is baffling. In reality, it is merely a means to keep two people bound after sexual intercourse so that their offspring has a better chance at surviving in the harsh environment. Nothing more nothing less. Now the mechanisms WITHIN love as an evolutionary construct is extremely complex - but it doesn't go beyond evolutionary construct.
c] What would life be like is love didn't evolve?
If love didn't evolve, human beings would have a very tough time surviving as babies. The process of longitudinal maturation would simply not exist as a mechanism for humans. We would have to have evolved with maturation levels earlier than 18-20 years old which would be deleterious to the development of our brain. The reason why humans can take such a long time to develop from children to adults, relative to other animals, is because we have parents that love each other and love us. We have evolutionary guardians, which supply us with protection, sustenance , and shelter. This allows for humans to develop complex and cultured minds and consciousness, without having to fend to survive in harsh environments. Take away love, and you are left with an organism that has to look for food, shelter and protection. Not an ample environment for brain expansion, and development. Arguably, we wouldn't be the intelligent species we are today without the mechanism of love. Its an evolutionary FACT that children/babies fall IN LOVE with their guardians. They develop a social tether to their guardians as a means to explore their environment. When they feel safe they will explore their surroundings, and when they feel threatened they will retract the metaphorical tether's distance back to their guardian. If they didn't love their guardian or vice versa this synergistic relationship could not happen.
Well that is merely one reason why love is integral in our evolutionary history but there are a plethora of reasons why we need to love to survive and be the species we are today.
The contradiction between social love and evolutionary love: A Modern Conflict
d] What I think about love as a cultural/sociological construct
I could literally write a 30 page essay on this topic, and Im sure one day i will get to it, but I will keep it short for the sake of parsimony and an appeal to occam's razor.
Love in our day and age is still ultimately evolutionary but people don't view it as that. We have develop and construed ideologies that ascribe love to some ephemeral metaphysics which take away from its fundamental constituency. We have reached a point in conscious awareness where we can ascribe certain expectations to love and make it fall under conditional statements. If you do a,b,c than I will love you x,y,z. We have ultimately detracted from the initial use of love and now have these conditional expectations which make love LESS stable. We want people to have "unconditional" love which is simply not possible as humans are conditional beings. We want those who love us to "love us" with a GOD LIKE metaphysical vigour, simply because of our metaphysical ascription to it. We have reached an impasse in our modern 21st century society in terms of love. We want god-like unconditional love from semi intelligent evolutionary ape organisms. Its not possible and this is one of the many reasons why I believe a lot of love doesn't surpass the honeymoon stage. We let the modern zeitgeist of love influence our conceptual paradigms of relationship expectations. Not a very realistic approach. The advice I ALWAYS give to people in terms of love is this: lower your expectations or you'll get hurt. Your evolutionary disposition (love emotions) are not meant to handle the expectations that we have placed on 21st century love.
Lastly, we have developed this belief that love is supposed to last forever. This is simply not the case. We have been developed evolutionarily to have our love last as long as offspring maturation, after that it becomes maladaptive. This is why divorces are rampant. But I don't think it is an issue. We aren't supposed to last that long, why fight it? Someone told me once that relationships have a shelf-life. That really struck a chord in my life. Its a very true statement and does not go against any evolutionary train of thought.