My wife was in a relationship with a woman before we met and married. She identifies as bisexual but as others have already posted, straight / gay is not a black / white thing. It's a continuum with a lot more grey than black or white. That said, it still was after many years of marriage when I finally confessed to my wife my desire to dress and transform. I'm not sure why it took so long for me to do so, that's another posting altogether.
My wife finds that being sexual with me transformed into Paula satisfies much of her desires to be with women. She often calls Paula her lesbian girlfriend. Sometimes she modifies that with the word "sl*t" between lesbian and girlfriend. We have both talked about how different our sex / lovemaking is when I am dressed. I know I am more attentive. Also, I want it to last longer. She tends to be the aggressor which is wonderful for me adding to the fantasy of it all.
So, question is does a GG need to have a shade of bisexual grey in her in order to full appreciate her crossdressing husband / SO ?