Well you need tell him your feelings
I think I'm in love with my close friend who told me he is gay....& I'm a girl?
I can't; it would probably ruin the friendship
Well, humans are humans, and there are some who believe that, no matter what your sexual preference, if it's true love - then things like gender just fall by the way-side.
Statistically though, I think there's a high probability that this type of relationship won't work. Not being cruel, just realistic.
I would consider this very carefully before investing emotionally. But hey, if it's what's in your heart - then go for it. The alternative is living the rest of your life wondering "what if..."