Hi Kelsey,
You will find when you ask that question here it is quite polarized into two camps "must tell (liar, liar pants on fire)" and "you will know when you are ready to tell". Personally, I told my wife but I had to because I reached a point of "emotional no return" and if I did not well just saying . . . I was heading for a very dark place. However, if it were something I did, enjoyed it for a moment or two then could put it away and continue functioning as a loving, dedicated and supportive partner . . . I doubt I would have told her. However, in my case I was becoming non-functional and it was bleeding into my relationship in other ways (depression, anger, resentment frustration and all around D-baggery - I was not a very nice person to be around).
Only you know when it is truly time to tell your SO and how to go about that. Some do it face to face, others via letter (Jen has an example in her signature block I believe). However, the key thing to remember is that once that bell is rung, it can never be silenced and this thing is going to go one of two ways: (1) acceptance on some level or (2) your walking papers. Should you choose to tell her some day, then communication after the fact is key to ensure things stay on an even keel. A while back I started a thread about communication post-tell to which many added great information which might help you should you decide to have the talk. http://www.crossdressers.com/forums/...couraged/page2
Cheers
Isha