Twink, l rarely post but just had to after reading your post.
You have had an awful shock l know just the kind of thoughts you have running thru your head. You see l've been there. l have been with my DP for 18 years and yet l have known about his cross dressing for about 17 of those, he was quite honest and up front about this part of his life quite early on, l am the only one in the world who knows. To find out when you are way into a relationship with DCs is something else all together though, so l can understand your shock and worry.
l doubt very much whether your DP is gay or wants to be a woman. If he is cross dressing he has more than likely been to some extent experimenting for most of his life. My DP has memories from childhood of dressing in sisters and mums clothes when he was alone. Quite often cross dressing has nothing to do with sex and is quite seperate a kind of stress relief for the dresser. Many x-dressers do not come across as feminine but often have an enthusiatic appreciation for well dressed woman in the public eye eg: in my DPs case anything a certain ex countdown presenter wears
There is no 'type' of man you could identify as a x-dresser, they come from all walks of life and make it part of their and their partners lives to many different degrees. The dressing is often cyclical, its goes away for a while and then becomes a need during periods of stress or other factors can trigger.
In your instance the most important thing is to talk to your DP about what you have found. You will want to know, how long, when, what etc many wives/DPs need to know but then need some time to process the information and how you feel about it in the bigger picture of your relationship. For me l accept it is a small but important part of my DPs make up, it is not worth ending an otherwise good relationship over. The Beaumont Society can help you if you need someone to talk to - thats the most difficult thing l cannot talk to my Mum, sister or friends about this.
Lastly l would add you need to think about boundaries - whether DP can have personal time in the home to dress, do you want to see him dressed or help him, can he purchase some clothes and keep locked away in the home, how to ensure the children are not exposed to any situation etc etc
Good luck and keep talking