In dealing with a teenager who may be falling "in love", I've had to recall what the "in love" feeling feels like abd what it means. And try to convey the honest truth that real love is not an emotion or feeling.
So I resorted to Gary Chapman's "The Five Love Languages" for the definition of true love:
"That kind of love requires effort and dicipline. It is the choice to expend energy in an effort to benefit the other person, knowing that if his or her life is enriched by your effort, you too will find a sense of satisfaction - the satisfaction of having genuinely loved another. It does not require the euphoria of the "in love" experience, In fact, true love cannot begin until the "in love" experience has run its course.
"In love" lasts about two years. It's what remains when it is gone that really counts as love.