I have known this girl for ages, and always known she amazing in every way. But she was going out with my best friend, and I was with my girlfriend.
Well they split up and I'm still with my girlfriend... and I'm crazy about this other girl. But, this other girl is still in love with her ex (my friend)
I know I feel stronger for this other girl, but if I did finish my current girlfriend, all my friends would take her side, and I would be left with nobody. And then this other girl wouldn't want me because she is in love with my friend.

Any advice?

Sounds like a lot of drama. How old are you? If you don't love who you are with, you shouldn't be with her, and you shouldn't have been with her in the first place. You have the knowledge that this girl is still in love with her ex, a.k.a. your best friend. Why don't you respect how she feels? She's just been through heartbreak, why don't you give her some space instead of trying to conjur up feelings and confuse her or cause more hurt... Wait until you know that she's for real, or 'the one' for you, until you try to get another woman's feelings invested in a relationship with you, just for you to break it off.

It's really not okay to stay with somebody because if you left them, you would have nobody. That's called using people.

Deal with one situation at a time, and put any new relationships on hold until you do.

If you decide to split with your current girlfriend, allow her the dignity and respect of doing it properly and honestly.

If girl #2 eventually becomes available, then by all means pursue her, but not until you are available, and she is available. Meaning she has split with her boyfriend, for all the right reasons as well.

You don't love your girlfriend. You shouldn't be with your girlfriend.

Honesty is always "number one" in a relationship - you're not being honest with her by staying with her while you're "in love" with someone else.

The girl that you're with should be the only one for you.

In my opinion, you need to let your current girlfriend go, she deserves to be loved by someone who knows she's the best thing since "sliced bread."

You don't love your girlfriend. You shouldn't be with your girlfriend.

Honesty is always "number one" in a relationship - you're not being honest with her by staying with her while you're "in love" with someone else.

The girl that you're with should be the only one for you.

In my opinion, you need to let your current girlfriend go, she deserves to be loved by someone who knows she's the best thing since "sliced bread."

I agree with HistoryChick completely if you don't think you can be faithful you shouldn't be with her. The fact is if your thinking about another girl while your with a girl fact is it could be common, but the fact your seriously thinking about it maybe you should just not hurt your current girl friend and let her down easily.