Love is obviously important to a set of genes existing within us reproductive machines. Without the feeling, the genes can't be sure that they will exist. Actually, they don't give a damn, they're just chemicals. They just have to have coded for an organism that cares, or else they wouldn't exist. Get it?
Any genes that don't code for the perfect chemical balance that causes love, then sex and reproduction, do not survive because they don't get replicated. Culling the herd.
We humans also love those we don't have sex with. We are social creatures. Our evolution lead to a strategy of working together. As one, or even as small families, all we could do is hunt, gather, have sex, and exist. As part of a larger humming organism, each of us may specialize and produce much more on the whole. In order for this to work, we have to be social.
It also means that our mates aren't just quick lays. It means we love them forever. We work with them to raise our progeny and ensure the survival of our genes (if our ancestors hadn't, we wouldn't exist). In that same vein, we do better for ourselves if we work together.
So this Valentine's Day, go out there and love your closest companions, and your friends, and your family. They are what make you human and special. Don't lose them.