I'm guessing you ask for fear of upsetting your friend if he does agree to go out with you? I would say she has her own issues--chasing multiple boys while claiming to be a lesbian--and that you shouldn't let those get in your way.
Normally, I would not even think about asking him out...
I'm a bit confused. Normally you wouldn't think of asking him out becuase...
your friend also likes him?
you believe the guy should do the asking?
I say just try to get to know this guy as friends, and if it develops into more, great, and if not, then you've saved yourself some possible trouble.