I feel for you. I really do. I remember being a lesbian and the thought of some guys penis in my woman. I was repulsed and discusted. Not to say you are, but there is no shame in that.
I also remember the trauma I put my wife of 5 years through when I came out as bi. She had very much the same reaction you are, bless her dear dear soul. I still weep over that. I would gladly have her back as one of my partners but I am now commited to a life long deep friendship with her that has been 11 years now. She keeps me on my toes with her questions and blunt honesty about her feelings towards poly. She has never and will never understand it.
When we broke off our "V" (her and my now husband), it was because I needed to follow my heart. I had had many relationships with men and had finally found a decent one. Now I have two primaries that are good good men. They do exsist. I'm sure if your partner finds one she won't settle for anything but the best. Especially considering her lesbian background!! You may very well be surprised. Be rest assured that there is a world of difference between male and female sex and intimacy. I for one have a lot of male intimacy in my life and still long for a woman, because of that difference. There is no way that she will be replacing you as far as I am concerned. It sounds, if she is at all like me, that she wants to feel whole in her sexuality. This is a good thing and can be temendously rewarding for you if you can muster up some compersion and also... This is a big one! Face your lesbian friends!
Good luck! I have more to say I think but if you read some of my past posts you may find that useful. I have talked about this before I think... ?
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