Falling in love is one of the most exciting, rewarding and scariest things you could ever do.
Once you're in love with someone, it's hard to remember how you lived without him or her. Of course, you were alive before you met this person, but you really didn't start “living” until the two of you met.
I remember when I first fell in love with my girlfriend; it was a very scary feeling, as I had managed to elude love for the entirety of my life before her. I specifically remember the transition from when I liked Mary to when I began to love her.
Mary went from being someone who made me smile to being the greatest catalyst of the happiness and joy in my life. She went from a gorgeous girl I met to the most beautiful girl I know. She went from my crush to the love of my life.
Everyone experiences love differently, and at different times. Even the meaning of love is extremely subjective, but I say for certain that anyone who's experienced it knows it's the best feeling ever.
To my best opinion for you to know that you are truly in love, most importantly is that when your girlfriend becomes your best friend.