You simply found what you wanted, and desires play with the brain in crazy ways. Your body change will make this desire more intense, and it shows physically. Just be careful because "falling in love" is not the same as "being in love". In regard to that, I like using the spanish words "enamorarse" and "amar", or portuguese "apaixonar-se" and "amar", because there is a clear distinction between them, and one does not implicate the other. You may find the difference as you mature.
Make sure you keep your friendship above anything else because there's always love in true friendship.