Say when they first meet, he only enjoys wearing panties & hose in the bedroom when they have sex and she thinks it's a bit kinky, but all in fun. But then over time he expands and wants to take it out of the bedroom and begin wearing outfits. So she adjusts her perception of what it means to him and she's OK with this as well. But then after a little while, he wants to begin shaving his body and get his ears pierced. At this point, she wonders if it isn't more than a harmless pastime, but she goes along (even though she misses her husband's body hair). And then he adds a wig, breast forms, hip pads, waist cincher, makeup. He plucks his eyebrows and his fingernails are permanently long and shaped. Perhaps he has permanent facial hair removal.
OK. So she still goes along (perhaps reluctantly now since she has no clue what's going on and her emotions about who her husband is are deeply conflicted) and she wonders if he's on his way to transitioning since he has changed his physical appearance considerably. She's afraid. He tells her no, he's not interested in transition and he doesn't see himself as a woman. But then he joins websites, perhaps starts chatting with other CDs, she finds that he has posted pics of himself all over the internet (in lingerie). The wife wonders if her husband is becoming more interested in men or other CDs than her. Perhaps she also finds an email or IM account or two, a facebook & myspace profile, and that's not counting all the hours doing this, plus the expense and the time involved in ramping up the presentation, the wardrobe, the jewelry, plus having professional makeovers & photo shoots. And perhaps a TG convention or two that take weeks of planning, shopping, and preparation, not including the time spent there.
So the wife begins to think that the CDing is far more important to her husband than she is, since he spends so much free time now (compared to before) on the CDing, the grooming, the shopping, the forums. And then he wants to begin going out regularly dressed, alone if she doesn't want to go with him, at first to TG safe places like alternative clubs, and then to mainstream places like malls, restaurants, & such. If they do go out together it is all about the stress (for her) and the excitement (for him), at least in the beginning since there is always a chance they will be recognized. The wife doesn't want her kids, her coworkers, his coworkers, their family, & perhaps some friends to know. Neither does he, but the excitement of going out supercedes the stress for him. And every time she's out with her husband and someone reads him and stares, she feels judged as well and her heart sinks a little and will continue to sink until she develops a tougher skin.
Oh, and he also wants to begin making GG & TG friends who do not know him in guy mode. He wants to experience being a girl with other girls. This is particularly worrisome for the wife at first, especially the GG friends, since the wife doesn't understand and she thinks that her husband is beginning to look outside his marriage.
This is what I mean by a wife having to stretch her understanding of it AND her support (if she doesn't want to stand in his way), so that she can keep up with her husband's growing expression. The wife never really knows when it will plateau since to her, it's been a continual expansion since day one, when it was only just wearing panties occasionally in the bedroom.
Now presumably they talk throughout all of this and he continues to reassure her that he's not into men, he doesn't want to become a woman, and he does love her. But she still finds it difficult to come to terms with this since what he says does not match his actions (looking increasingly like a woman, adopting feminine mannerisms, perhaps working on a feminine voice, dressing in ways that appeal to men, wanting to spend girl time with other women), and that's not mentioning the fact that clearly, the expression of femininity has become by far her husband's preferred activity.
The wife has to make a leap of faith to even begin understanding what it's like to be transgender, since there is nothing in her own internal landscape to even come close to experiencing anything like this. Additionally, she needs to redefine her marriage, her own role in the marriage, her place in her husband's priorities, and even her prior understanding of gender and sexuality.
I'm not saying it can't be done. There are many wives & girlfriends (myself included) who do stay the course with their CDing SOs, and who champion their right to be who they are. But it does require many GGs to stretch quite a bit. There is a learning curve, and it is steep for some GGs. Add to this the typical CDer who finds it difficult to define himself and who doesn't necessarily discuss with his wife every single next step or each new purchase until after the fact, and this adds to the amount the wife needs to stretch and become OK with each new development.