The main reason why love often fails is our failure to understand and accept the paradoxes of love.
1. Frustration is an essential element in romantic satisfaction
2. Desire thrives on distance, and love longs for closeness.
"There is a complex relationship between love and desire, and it is not a cause-and-effect, linear arrangement. A couple’s emotional life together and their physical life together each have their ebbs and flows, their ups and downs, but these don’t always correspond. They intersect, they influence each other, but they’re also distinct. It is too easily assumed that problems with sex are the result of a lack of closeness. But … perhaps the way we construct closeness reduces the sense of freedom and autonomy needed for sexual pleasure. When intimacy collapses into fusion, it is not a lack of closeness but too much closeness that impedes desire.
Love rests on two pillars: surrender and autonomy. Our need for togetherness exists alongside our need for separateness. One does not exist without the other. With too much distance, there can be no connection. But too much merging eradicates the separateness of two distinct individuals. Then there is nothing more to transcend, no bridge to walk on, no one to visit on the other side, no other internal world to enter. When people become fused — when two become one — connection can no longer happen. There is no one to connect with. Thus separateness is a precondition for connection: this is the essential paradox of intimacy and sex."
I will end this, with one of my favorite quotes from Khalil Gibran - "Let there be spaces in your togetherness..." For love, marriage and any relationship to last and succeed, there must be a maintenance of individuality. Don't smother your partner, it is alienating.