Nicky, it's so cool that you went into research mode instead of just bailing out of the relationship. As you may have noticed, questions like that won't get you a single, consistent answer; ask any five guys why they crossdress and what they feel about it, and you'll get six conflicting answers. Some of us are just in it for the clothes, and as long as we can have some time to just sit around feeling comfortable in a dress, we're good to go. We don't need or want to feel like, act like, or be treated as women and we certainly don't want to become women. On the opposite extreme of course are the pre-op (or "never-op") transsexuals who wish they had been born a woman and are either on their way to the full snippage or, if for whatever reason they can't do that, at least want to get as close as possible to purging themselves of all Y chromosomes. Somewhere in the middle are the majority - some like to use a "female" name when dressed, some believe they have two physically distinct personalities depending on whether they are dressed, some just want to sit around at home and feel pretty, some want to go on the town and be admired.
There's really no way for us to tell you where your man is on that scale - and he may not even know for sure himself. So together, you'll need to find out his needs and your limits. How comfortable would you feel if he decided to change his name to Sally and live full time as a woman? If the idea scares you to death, don't count on that feeling going away in 5, 10, 20 years... set limits NOW for what you are comfortable with NOW. If he needs to take it much further than you're prepared to live with, it would be brutal on both of you to pretend otherwise.
Which leads me to a topic you probably already know, but needs to be emphasized: Whatever level of gender identity he deals with is not just a passing whim or a hobby he can give up like stamp collecting. It was a part of his nature before he knew it, and if he's like the rest of us he was probably scared and confused when the feeling first manifested. Some few have tried and succeeded to give it up entirely, but not without terrific emotional cost and most of us have tried and failed many times (read up on "purging").
As the happily married CDing man of a wonderful woman who understands and accepts, even if she's not particularly thrilled about it, I hope things work out for the both of you.