one question, one suggestion:

- Does your friend know you like her? I am assuming he doesn't.

- If he is your good friend, i would suggest you back off. You can be friends with her but stricly remain as that. If she however is interested in you then she has to make the first move. This is a given if she knows that your friend likes her too. So don't let her ruin ur friendship. Personally, the friend would be more important to me at this stage.

Hope it helps.