First what sticks out to me is you were drinking when you brought it up. I have a number of straight (REALLY STRAIGHT) friends who will flirt with me when they are drinking because they know I am safe. They also know I am bi-and several have asked me if I would ever go for them when they were drinking (general answer is NO NO NO).
He very well could be thinking "wow that was daring of her I wonder if she regrets it".
Then when you clarified he might be thinking -"God she's gonna get me killed (by hubby)"
He very well may have NEVER CONSIDERED the possibility before.
He might have used it as a fantasy-but never thought it was a REAL possibility.
Either way he might feel like he just needs some time to process the whole thing. Heck even single people getting offered a relationship from a single friend need to think it over first because there is inevitably risk involved.
Check out the thread on "the thirdness of being a third" (think that is the name either way it's close to that) by Ceoli-it might enlighten you to some of what HE may have to "look forward to" so to speak in this situation. Well worth the read anyway.
I would give him his time away to think. Then let him know briefly when he returns that "when you are ready to talk I'm looking forward to the discussion".
Then when/if he's ready to discuss-ask all those questions you said in here!!!
"Love As Thou Wilt"