As an elderly person who struggled with this in secret my entire life, I can't even begin to imagine what this would have been like for me. My hat's off to you... as the saying goes.

Do you get the impression your son may eventually come out as transgender? Or do you imagine he'll continue as a crossdresser? Either way there's a very nice forum website I could recommend (just in case you're not already familiar with it.) It's "Transpulse":

Transpulse & TransGender Pulse Forums

There are, of course, other trans websites. But this one seems to me to be the most active. (I'm not a member, by the way. But do snoop there fairly regularly.)