I think it is important to point out that you are not in love with HER. You are in love with a little piece of her.
I am not doubting that you love the aspects of her that you know. However, if you have not dated her (or at the very least taken her on trips that were multiple days long) then you really don't KNOW her. You know either her persona (or for those of us who don't have a persona, then you know an idealized/on her best behaviour version of her).
It is really easy to put your best face forward for a few hours at a time. This is what we all do to allow our suitors the experience they deserve as they step out of the real world for some genuine TLC. You get our undivided attention when you arrange for a liaison. The focus is you. We are attentive, caring, loving and genuine. We are not distracted by our personal day to day life. But that is not possible to maintain 24/7.
As much as it pains me to say, my suitors get treated far better than the people in my personal life do. Those in my personal life get all the awesome stuff too.....but they also get all the crap. When I'm having a bad day/week/month.....they know it!
I don't believe you were wrong in telling her you love her. I believe we should always be comfortable and free with expressing our emotions. However, I really believe that you have taken the few pieces that you know about her (which I am sure are genuine), but then filled in all the blanks with your own fantasy of what you would like her to be....or think she could be based on the slice of her that you do get to see.
What are her hopes and dreams? What does she believe happens after death? What is her greatest fear? What brings her the greatest joy? How is her relationship with her family? What is her personal creed? What organizations does she belong to, and how much time each week does she spend with them?
I'm guessing that you don't know the answers to most of those questions - at least not in great depth.
I'm just trying to let you see that you are not really in LOVE with her. Infatuated ~ quite likely.
More likely - you are in love with the way you feel about yourself when you are with her.