M.P.
I think it's very important that you deal with this issue. It will haunt you until you do. I suggest that you first discuss it with your counselor by yourself so that you can synthesize what you want to say to your husband. You want to make the issue specific to your feelings. I'd start with your feelings as they relate to your husband.
Your feelings about his friend and women who do this may change once you know how your husband deals with you and your feelings over this issue.
For me the bottom line is how my husband responded to the "friend's" suggestion. Did he meet the woman's friend? What is his rationalization for doing so. But then I'm a firm believer, based on my own unhappy experiences as well as seeing the violence and just plain pain that happens when a married but yet not divorced person becomes involved with another woman/man, that no one should start dating until their divorce is final.
As to your second question about it being normal: There is no such thing as normal. Everybody is different. Yes, there are women who would offer to do a set up as you describe. Because she didn't know you she doesn't have any sense of loyalty to you but does to your husband. The fact that he's already cheated makes it more likely to happen. He's shown that he's available and he says he's getting a divorce. He doesn't have to have said anything about you. "Everybody" cheats these days. Today it seems that most people start dating once they decide to get a divorce if they haven't already. I've been single most of my adult life and learned that I had to be really careful because it has been my experience that more men cheat than those who don't. I hope that faithfulness is more common in a larger world than the one I live in. (I'm a retired police officer.)
To cheat was your husband's choice. No matter how horrible you might be he still had a choice and he chose to cheat rather than deal with whatever was making the opportunity attractive. I worked with an officer whose wife was an alcoholic and frequently called the office to check up on him. A couple of times she even called me at home making accusations. Now if any wife would provide her husband an excuse to cheat it would be her. He did not cheat as far as I know and gossip is rampant in the force.
I'm not saying you're horrid. I'm saying that blaming the wife is just an excuse. Your husband's friend did not need to think you are horrid or blame you in any way. She may even know that your husband on his own would welcome the opportunity. And....not all husband's blame their wives.
If your husband said that he was unhappy in his marriage then he chose to deal with his unhappiness by creating happiness elsewhere. Being involved with someone else is much simpler and more exciting than being involved with your wife. Apparently he's returned and is now learning how to relate to you. That's a good sign. It is important, however, for you to have your anxiety answered. I heard Dr. Phil say to a husband who had returned from cheating that the natural consequence for him for his actions is to be ready to answer all of her questions, the same questions over and over, for years to come. Your husband will probably need help in learning how to deal with that. Another good reason to bring this up in counseling.
It seems to me that you have several issues that you need reassurance about. And I expect that you will continue to be angry and anxious until your husband shows you thru his ongoing faithful relationship with you that he's different now than he was then. You need to ask questions and he needs to answer them in a compassionate way. A counselor will help you both learn how to relate with each other in this circumstance.