I agree with this- you, and only you know, when and how to tell her. There isn't a one size fits all way to talk about this, and if you're not comfortable talking about this, it can be extremely hard on both of you if you just open up one day. And it can be done by showing, it takes patience, but my wife figured me out before we were married just based on how I reacted when I dressed up in front of her. You can't treat it like its a big joke, but you don't have to go into this like you're about to deliver the Emancipation Proclamation if that just isn't you. Take your time, be fair to yourself as well, and do it in your way, especially if this isn't something you do every day or think about all the time. Trust your instincts on this, and know that no matter how hard you try, you can't make your SO like this. But you can make this work, just don't push too hard, too soon.