Help! I'm so confused. I think I love a girl, but I'm fairly sure I'm gay.?

You say that "when I think about never having a relationship with her, my heart kind of pangs" It sounds like you will always have a lifelong relationship with her, IMHO as a best friend. You have so much history together, why would you potentially mess thing up by changing the dynamics of your relationship. Yes, you are in love with her, friendships are loving relationships too, they are just not physical relationships. Just think what would happen if you sleep with her and you decide that it's not what you want, and it confirms that you are a gay man? You may really hurt her, and I guarantee your relationship with her will never fully recover, or will cease to exist. One night of indiscretion, can erase all that you have built over the course of many years.