I'm single right now, but both of my previous girlfriends not only knew I watched it, but also knew I had been sexually active with TG's too.
The more recent one found porn I had watched on my computer which caused her to find old emails from a transgender girl I was having sec with before we dated. She confronted me about it and was really weirded out by it. I thought it was hypocritical of her to be so upset because she would watch girl on girl porn and she wanted to experiment with women. Anyways that relationship lasted about 1 more year.
The girl before that knew about it and not only did she not mind, she was into it. She actually wanted to watch me with a Tgirl, but it never happened.
Next time I'm in a relationship I'll be more careful if I can tell the girl wouldn't be into it .
But truthfully I hope my next gf is a transgender woman, I like their personalities better.