I wouldn't go there if I were you. First off, she's married. Secondly, you've been friends for 10 years. If you felt a real attraction to eachother you probably would have got together years ago.
Perhaps she feels stuck in a rut and is enjoying some other male attention from somebody other than her husband. You don't say if you're in a relationship? Perhaps you're both lonely and so things are going further than they should.
I think it would be a big mistake to risk a great friendship, but that's just my opinion. But then, can you go back to being just friends after all the snogging etc. Have you asked her outright what she wants and exactly what feelings she has for you?
Perhaps you should leave her for a while to work out what she wants. Just cool things for a bit, so that you can examine your feelings also.
Good luck with whatever happens!