As a young adult I've had a few mild sexual encounters with women and decided I didn't want to do that anymore. I've been married for 7 years to a very sexy man, but have always thought of being with women sexually. I have never, and will never cheat on my husband. Is it normal to have these desires towards women?
I think you will need to be firm in deciding again that you don't want that especially with your lesbian friend if she makes any further advances. If you did something with her I think you would feel you've betrayed your husband & marriage.
And really, what is the difference between and extramarital affair with either gender? It is about betrayal & broken trust either way. Don't in your deepest imaginings think that because it is same sex, it is not cheating.
Also - back to the bedroom - are there things your husband can do that you would like from a woman? Sounds like you've got a good thing going there.