What's it like changing from "in love" to "love?"?

I was thinking of the sentence, “I love you, but I’m not in love with you,” and it made me wonder about the transition. Do most people lose that “in love” feeling and end up at just “love?” Do some people always keep the “in love” feeling? Is it bad to lose “in love?” What does the transition feel like and how do you know when you are no longer in love?

What’s your experience with this? Have you been able to maintain that “in love” feeling or not? How did you know when it was gone? Do you expect it to go or stay if you have a good relationship?