depending on your friend, this may not always be a smart thing to do.  most guys (especially married men) are not automatically inclined to stray into the hobby.  sometimes when they do it's because of friends, colleagues at work, or even random business associates (like the celebration that comes after signing an important contract!)

depending on how grounded the guy is he could end up getting his ass into a bind.  there's also his family and children to consider (if that applies) and a whole host of secondary people around him that may be affected

if he's single, fuggadaboutit!  ... you'd be doing him a favour!  

LOL

"His S/O knows mine real well so this has the potential for a major disaster"

 I think that says it all. If you aid in his journey into the hobby and his SO someday finds out it is you who will bear the full wrath of everyones anger and loss.
 Avail your friend with the tools but don't set yourself up as entertainment director. After he has hobbied a few months on his own and successfully avoided being caught maybe then you can plan a "Golf" trip together.

I mentioned my hobby to a friend who was going through a divorce about a year ago.  He thought the hobby sounded great at the time especially for married guys.  Now he has a new SO and I find some tension when I mention the hobby to him.  Don't know what it is, but he just sort of changes the subject.  

Now I wish I'd have kept my hobby to myself.  As time goes by his SO and my wife are getting aquainted.  I wonder what he told the SO back in the days when she was just a new gal to bang.  You know, when they first met he doesn't see her becoming anything but a hot bod and just starts yaking away about this friend.  Then the hottie becomes SO and starts to meet his friends and so on....

Since your friend knows about your hobby you have gone to the same place I went all ready.  But I might suggest you not intorduce him to your ATF if he doesn't know who she is all ready.  I'm starting to think the less that is out there the safer it is.

Wouldn't do it.  High risk all around.  But the horse may be out of the barn.

Your friend already knows you Hobby.  That's the dangerous part.  Now, if he want to...  Why not?

Be careful sure, but he's not going to tell, so
the chain stops in Orlando.  And, he'll go from
a good friend to a very good friend. Go for it.