Discussing Crossdressing with Your Partner

I’ve been crossdressing for a while now, even going out once or twice (long drives, fetish clubs) and have told a few close friends about it. However, I feel the need to tell my girlfriend of five years because I’m considering moving in with her. The issue is that during one staff member’s pimps-and-hoes night, she wanted all the men to crossdress. I almost went until money issues got in the way, but when I told her I was thinking about going, she wasn’t too pleased that I wanted to go alone as a man. She seemed more concerned about my underwear than the outer garments. This puts me in a position where I know she wouldn’t like it, but knowing she would hate even more if she stumbled upon clothing that blatantly isn’t hers, along with all the makeup I’m soon going to own (she barely uses any), so she’d know it’s mine.

P.S. Can anyone recommend a good makeup advice site for complete novices?