Wow Emerald, why couldn't you ask something easy like the meaning of life?
OK, here goes. A crossdresser is a transgendered person who can be happy with occasionally satisfying the need to live as a member of the opposite sex for varying periods of time. I do tend to agree with Lyric that it is an action, it does not describe the person. Through association with Southern Comfort Conference and running the Big Brother/Big Sister program for conference newcomers for a number of years, I've met TG people from all over the world and the stories are as varied as the people. Married, single, living together, straight, bi or gay, supportive spouses, ambivalent spouses and spouses that find their cross gender behavior totally unacceptable, they all share one thing in common. A duality in their person. Some can be happy with only living that need once a year at a conference, some on a monthly basis, some weekly and some as often as possible.
Perhaps a better question is what causes the crossdressing action. Most of us know that a fetus, whether XX or XY starts out in the womb female. At a certain point, the XY chromosome causes a hormone wash that masculinizes the fetus. If the hormone wash occurs at the correct time, the person will be single gendered male. Mind and body agree. But if the hormone wash occurs late, the brain continues developing as a female brain until the wash does occur. Let the wash occur a little late and you have a bigendered person who has both a masculine and feminine nature, i.e. a transgendered person who crossdresses. If the wash occurs even later, you have a person with a masculine body at war with a feminine brain, i.e. a transgendered person who has no choice but to transition so that mind and body match. I wish could cite the source on this but I know it was based on Dutch research that shows that certain parts of transsexual brains match those of genetic females.
Now for those who said their wives or girlfriends were at first supportive but have backed off some, as a suggestion, check your own behavior. Sometimes with coming out to someone and not having to keep your secret inside, their is a sense of euphoria that can cause you to behave a little differently. A friend once described this, for lack of a better term, as "The Attack of the 16 Year Old Girl." Her statement was that you begin behaving like a teenage girl and that your significant other does not know how to handle it. She would expect this behavior from a teenage daughter, she does not expect it from you. I know as after my first conference I suffered this attack myself. Having gone from NEVER appearing in public on Wednesday to walking into the Hard Rock Cafe on Thursday night, it was almost like a drug. After a period of about 3 months, my wife was about ready to kill me or divorce me depending on whether she could reach a weapon or a lawyer first.
If you find that your behavior has changed to something like this, back off a little and give them time to adjust.