From a scientific viewpoint it would seem that the emotion of love has evolved in humans because it has obvious survival value for the species. Love of men for women and women for men binds couples together, and this makes for better and longer cooperative care of their offspring. Love for children is obviously of extreme importance for the children because it will assure their nutrition, protection, and education. Love of children for their parents would seem to reward parents for the stress and sacrifice involved in rearing children. Love of is not exclusive with humans, and some animals and birds appear to be bonded by an emotion like love.
Desmond Morris has written many books about the subject of human evolution. He explains everything about us in terms of Darwinian evolution. His books are interesting, enlightening, and easy to read. Most of them are even full of illustrations. I recommend that you read The Naked Ape. Please refer to the e-notes Study Guide by clicking on the link below.
Of course, there are a lot of other ways to look at love. Love is a beautiful emotion, and poets have been writing about it for thousands of years. At least three-quarters of the popular songs are about love, and so are the movies. But your question seems to be asking about the practical, utilitarian importance of love in life; and the evolutionary explanation seems the best approach to an answer.