HERE is how you truly determine if its worth it
1) When you think about her, do you think about just getting with her?
If yes then don't, its not worth losing a friend over.
OR
2) Do you just like being around her and the last thing on your mind is 'getting with her'?
Then I would do it, but don't you dare try and hide it behind your friends back. Tell him first
#1 is what most relationships are, based on looks usually
#2 means it could really be a very good relationship that could last for a long time or forever
DON'T ever lie to yourself about which one it is just so you can convince yourself to do it. You know the answer and im betting its #1.