fall /fɔl/ Pronunciation Key - Show Spelled Pronunciation[fawl] verb, fell, fall·en, fall·ing, noun –verb (used without object)
|1.||to drop or descend under the force of gravity, as to a lower place through loss or lack of support.|
to pass into some physical, mental, or emotional condition: to fall asleep; to fall in love.
is definition #13!
While the phrase as a whole is extremely positive, it's rooted in something negative. We're all afraid of falling. It hurts. I'm still bruised from a fall I had Friday night, and I have problems from a fall I had six years ago. I really don't like to fall.
However, growing sounds much more positive.
grow /groʊ/ Pronunciation Key - Show Spelled Pronunciation[groh] verb, grew, grown, grow·ing. –verb (used without object)
|1.||to increase by natural development, as any living organism or part by assimilation of nutriment; increase in size or substance.|
Sure, growing has its own pains, but, to me, it's much more promising than falling. President Spencer W. Kimball put it this way:
"The love of which the Lord speaks is not only physical attraction, but also faith, confidence, understanding, and partnership. It is devotion and companionship, parenthood, common ideals and standards. It is cleanliness of life and sacrifice and unselfishness. This kind of love never tires nor wanes. It lives on through sickness and sorrow, through prosperity and privation, through accomplishment and disappointment, through time and eternity." (The Teachings of Spencer W. Kimball (1982), 248.)
Elder Lynn G. Robbins wrote a wonderful Ensign article about eternal love, which I recommend. He also pointed out being in and cultivating love is a choice, and to fall in or out of love connotes a lack of choice, which I completely agree with.
I'm not saying that I'll never use the phrase "falling in love" or any of its derivatives, just that there's a better alternative. Either way, I certainly look forward to experiencing it again.