A major part of love is commitment. If we are committed to someone, if I'm committed to loving you, then it's not possible for me to 'fall out of love.'
My students tell me, we don't want to love! We're tired of being loving! And I say to them, if you're tired of being loving, then you haven't really been loving, because when you are loving you have more strength.
The people I love, I'm committed to loving for the rest of my life.