The others have given the best advice - communicate and then communicate some more. Probably he has been hiding this since being a small child. I did from the age of 5.
May I suggest that you do not bring up his shoes or stash. Very intimidating, and he will tell you he will throw the stuff away and will be embarrased. Much better to mention you found this site (BTW how did you find us?) and got curious, finding out that most CDs are straight and family oriented. I can tell him that it is not easy - as he knows- but having a tolerant wife can help a lot. Suggest you set up some giudelines - frequency of dressing, amount of money spent, going out and who else (if anyone) should know or might find out.
BTW I would bet dollars to donuts that his Mom knows even though he probably does not think so.