yes... love is smth which is not explainable...
falling out of love is very possible...
losing interest is possible also... but sometimes... we relate too much LOVE to a relationship...
think about it...
do you really think the word love still exist just because two 65 y/o couple still love each other???
it is their habit, memories, thoughts, and friendship keeping them together for that long...
love is a multiple level word that encompasses alot of things...
so... if you lack of smth... it would slowly deteoriate...