I am stuck in a very weird mental dilemma. NEED URGENT HELP!?

Relationships are freakishly complicated. I bet you have no problem understanding that... If you really love your girlfriend as much as you seem to, go and be happy with her, because the last thing a girl wants to be with is a guy who is depressed because of these feelings that every guy will have sometime in their life, but will be too afraid to admit later on... It's ok... You're ok! If your girlfriend has been with you for this long, I have no idea why you are willing to let her go for some other chick, you might have a chance with... stop thinking about your best friends girlfriend, because that will more than likely lead to trouble and broken relationships... The other alternative that I would take, in my opinion, is to ignore all options, break up with your girl, and be single, making your life less complicated... But if you really love her, and are willing to do anything for her, then that should be the girl for you. Even if you doubt she's the one, not everyone is perfect, and anyone can do something to make a relationship improve... So keep that in mind, and be with your girl, other than that, being single is a sure way of getting out of your funk.