well since your best friend doesnt even know if shes gay, then i would find out how she is really feeling. You said she has feelings for you but shes not gay, although having feelings for someone usually means they're attracted to you, thus making her gay/bi. Now onto your girlfriend-- is she still with her boyfriend, and if she is gay has she told him, or do you and her keep your sexual relationship private? If I were you I would stop all fooling around with your best friend. You say you love your girlfriend more than anything, so treat her like you do and don't cheat on her. Figure out if she wants to be with you or her boyfriend, and if she wants to be with you and you want to be with her then keep it that way. You have to make a decision on whether the feelings you have for your best friend are serious like the ones you have for your girlfriend. And if you know you love your girlfriend in a more stronger, serious way, then be with her.