Consult your friend first
Before you go sticking your tongue in stray orifices (like her face, ya pervert) talk to your friend and tell him how you feel. Take solace in the fact that there's no conceivable way it can not be awkward.
"Directly!" chimes in the good doc. "Ask directly, say the words. Inferring, by definition, leaves room for interpretation. Even if it may be uncomfortable, make your desires and intentions known. Though this might not solve everything, it's a good first step."
Objectively, it's a weird thing to go after someone who definitely had sex with your best friend. Eskimo brother be damned! Wait, is it still kosher to use the term "Eskimo"? Wait, is it still kosher to use the term "kosher" when not talking about food blessed by a rabbi?!