You made the decision to share any info with XGF. I am not buying that she out of the blue made a sexual advance. Real life just doesn't work that way unless she has some kind of serious character flaw. It was an inappropriate offer at best.
Your answer should have been an emphatic "NO" and not some mamby pamby "Oh, if I did that it would be the end of my marriage" thing. Your answer, IMO, is sending her a message that you are interested and that if you could you would...
I think it might be best if you break off any contact with XGF.
“Things turn out best for the people who make the best out of the way things turn out” ― Art Linkletter
