I'm a little late in reading this Post, but would like to take the opportunity of adding my thoughts, which are based on my experiences as a husband that enjoys cross-dressing.
Firstly Katie, it's very sad that you only found out about this side of her Husband after 20 years. No wonder you're worried and unsure of the future.
I've been cross-dressing from early childhood and can say with some certainty, that this is something that your Husband (nor any Doctor) can stop. It is the way that some of us are born and I look at it as being one of hundreds of shades of grey, between black and white, or between Arnie and Kylie. We cannot help how we were put together.
Over the years, I have met dozens of guys who like to crossdress, some of whom enjoy wearing a skirt around the house while others were actually trans-sexual and have gone on to have surgery. The vast majority are the former and simply enjoy the feel of feminine clothes. After all, they are much more comfortable and are made from much softer fabrics.
I myself enjoy dressing fully as a woman and going out to restaurants or quieter bars, as I am very fortunate in be able to "pass" and not attract unwelcome attention. Whether this is what your Husband eventually desires, I can't say. What I can say though, is that I chose to be totally honest with my wife before I asked her to marry me. She was shocked, confused and we both shed many tears. I thought I'd lost her. That was 20 years ago and gradually, over the years, we have both developed an understanding that has seen me go from a guy wearing a skirt in secret at home, to a well-balanced, loving and faithful Husband who is able to release his feminine side, openly and without feeling ashamed or frightened of losing his family.
I think all that I'm saying here, is that the only way forward is for both to talk to each other, openly and honestly. Try to agree compromises and to understand each others feelings. The Beaumont Society is indeed a great source of information and support for wives. No-one fully knows what the future holds, but I honestly suspect that your Husband is no different to the tens of thousands of other crossdressers in the country, who just want to be accepted as a guy that needs to express his feminine side. Trust me, every man has one, but it takes a real man to admit it.
Wishing you both the very best of luck.