As a lesbian, let me see if I can facilitate this.
dbrose said:
Wow. Okay. That might explain why she's been so distant.
Relationship failure is more likely the reason. You two got together for whatever reason, which means she was digging whatever you were serving. She enjoyed your company, liked being with you, and chose to act on those feelings. If she's being distant, there's a chance the magic is fading, or something has happened in her life recently.
dbrose said:
Should I talk to her about this?
Communication is key for any relationship to survive. So I believe, yes, you should communicate your feelings and thoughts of a stagnating relationship to her (tactfully and kindly, of course). Be prepared however; such a discussion is a fork in the road. If she really is getting tired of the relationship, this could be an easy out for her. However, not talking to her will only delay the inevitable. Talking with her could even save the relationship, too, so it's not like you're doomed here.
Now, with the basics out of the way;
dbrose said:
So I was helping my girlfriend with her computer earlier this afternoon and I noticed a book on her shelf entitled "The Best Lesbian Erotica."
I repeat what I said earlier; she chose to be with you.
She does not however choose what she's attracted to. Attracted to women or not, she's with you for her reasons. That book could be on her shelf for any number of reasons; A friend left it at her place; she was curious behind the appeal of lesbian sex culture; she needed "reading" material because the porn industry is a disgusting place for women to find things to get off on. The list of possibilities can and does go on.
So don't jump at your assumptions. Communicate with her, and you may find your relationship blossom. But if she's being distant because things aren't working out on the very basic level, then it won't matter if your girlfriend is attracted to women or not.