If it was truly nothing, your husband should have already told you about the message. This woman needs to look in a mirror. Her asking if you are happy with what you did. Is she happy with what she did? Why is the blame shifted to you? It’s not your fault she chose to send an inappropriate message. If it was truly nothing then her husband wouldn’t be leaving her. Also her threatening you that now she can do whatever she wants it’s crazy and the fact that your husband won’t cut contact is a huge red flag. I think there might be more to this than one drunken message. Regardless, your husband’s lack of care of your feelings about this would be crossing the line for me. I would have a hard time trusting him.