WildHorse03, you can't imagine the level of sympathy I feel for you. I'd give you a hug if I could. I, too, have been in love with a little girl. Two, in fact. When I was young, I fell in love with a 3 year old, and then later in my life, a 10 year old. I've always found this love harder for me to deal with than the sexual attraction, which I'm sure many would find very strange. It's easy to dissociate yourself from sexual attraction, but love is so much stronger and more pervasive.
When she masturbates in front of you, wanting you to watch her change, etc... immediately discourage her from doing so in simple but firm way. Don't make her feel any shame or make any kind of a big deal about it, but let her know that such things are inappropriate behavior. Immediately change the subject afterward or otherwise divert her attention. Don't think about it at all either while you're still around her. This is for the best... grown men and little girls can not be together in this way, and she can't be receiving mixed signals from you for her sake.
The fact that she's acting in this manner for you must make it incredibly difficult to deal with. If you can handle the intense feelings you have while you're around her, do everything you can to enrich her life in a completely platonic way. Use your love to become a wonderful male role model for her. Play with her, take her to the movies, help her with her homework. If you can use these feelings to improve her life, I say go for it.
If this is too difficult for you to handle, I recommend you distance yourself from her. If you do, these feelings will eventually go away, but it will be very hard to deal with for awhile. If in doubt, distance yourself from her. You love her, and I'm sure wouldn't want to cause her any direct or indirect confusion or anguish.
Whatever you do, don't kill yourself. We have been dealt a rough hand in this life, but we can overcome the confusion, pain, guilt, and heartache that we all experience when we fall in love with a little girl. I am living proof of that. I felt exactly the same way you did when I was younger, but I had a great support system and have gone on to live a perfectly normal, happy, and fulfilling life. You will get past this, I believe in you.