Because love demands effort, it doesn't take long for love to become an impending responsibility rather than a blossoming blessing. Of course, you would do things for that special someone out of love, but because you are inevitably expected to do things, it becomes an expression of frustration rather than passionate affection. Doing things because you are meant to is very different from doing them because you want to.
Over time, as love becomes more demanding, you find yourself looking to friendship for a resource. It's times like these that friendship further demonstrates its value as an asset, one that allows you to just sit back without having to worry about all the qualms that romantic love throws at you.