Well take your pick you'll get a different answer from anyone you ask. Personally, I've considered what love is and what is required to make it work and last and this is the best I can come up with from my own experience....
Romantic love is placing the hopes dreams and desires of someone else above your own. Its a willingness to sacrifice and compromise to allow your loved one to fulfil the life they want. When love breaks down its because the other party doesn't share in this philosophy of giving and is unwilling to reciprocate the same spirit of generosity and puts their own interests first. Almost at once, resentment starts to grow and feelings of selflessness and sharing begin to withdraw.
When love works (and lasts) both parties realise the benefit in mutual sacrifice and continue to strive to allow each other to achieve what they want in life to the best of their ability, be it a career, children, a certain lifestyle or just emotional support; if its asked for its given without questions and in both directions. This notion is based on trust because its given with the knowledge that the same would be offered to them in return. So love in that respect is trust.
When love works, then this pact of love is seen as an entity, it exists, it has value. If love were an object, a ‘thing’ that we could see and touch we would never let it become neglected; if it were a shiny expensive thing of material value we would recognise its importance and maintain it, clean it, repair it constantly and value and treasure it. Because we can't see it, we can forget its importance, we let niggles and arguments fester like rust on this object we become concerned with other objects or ideals of less importance and become too busy to tend to our love properly. This 'rust' sets in and cracks start to show and eventually as with all things it becomes beyond repair and falls apart. However if we maintain it, look for and recognise the cracks and ensure they are repaired with our time and affection and compromise and humility then love can last and grow stronger and beyond destruction and last a lifetime.
Well that’s my view after some musing on the subject. Hmm my view of love seems remarkably like communism, mutual giving in the spirit of a greater good for all. Maybe that’s why it’s always been a nice idea but fundamentally flawed for me previously.