How many of you have read a biography of the Buddha? Siddhatta, the Buddha to be, romantically fell in love with his wife, Yasodhara. When their eyes met, that was it. In English we say, "love at first sight". It happens to a few people.
Why does it happen? In Siddhartha's case, they say it happened to him and Yasodhara because they had been married 500 life times before that life. I think they practiced a lot with the four Qualities necessary for a good relationship: faith, morality, generosity and wisdom - they were matched. They had romantic love, but what was it on a deeper level? It was a bonding on which they were developing the paramis together and this took place over many, many lifetimes.
When there is a deep romantic love which leads to marriage, Buddhism would say that's because that couple have been married before in past lives.