Ethical dilemma

I agree with the comments made so far. It sounds as if it started off as a few small gifts, but he has taken it to a new level. I suspect that he is becoming heavily dependent on your wife, and that his own wife will soon spot the signs that he is putting attention elsewhere. To me, she needs to reset the baseline, get it back to an occasional thing and tell him that the expensive presents are making her uncomfortable. Hopefully, he will get the message before he does something stupid and his wife catches him out. He might think that he is super clever, but the wifey radar might already be on full alert because us guys are rarely as clever as we think we are!
Agree totally, I am not comfortable with the relationship, but a few years ago, I was encouraging her to experience life with other men, he was very scared and reluctant, now it she who is asking me to be ok about it, her view is
that if she is sleepig around with other men, why not do it with someone who treats her like a princess.

This time she has brought home quite a few of his wife's things, that he asked her to pick, likely his wife will find it missing.

This dress is not new, she took it and wore it back home, her bf took the picture in the lift and she has already posted it to her facebook feed before she got home, saying "look at my new shoes and dress", this scared me, I told her, well she is not too concerned about it. She is planning to wear it to the temple this evening, so many people will see her there.

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Folks, what to do here.
Wife was out with her boy friend yesterday, who thinks that they are having an affair, she has told him that she is married but not told him that she is a hotwife, she enjoys the attention more than anything from him, it has been going on for about a year now. Problem is that for my wife it is fun and she tells me all the stories.
It appears that he is taking more seriously, and on each date, brings something for her, often they just meet for lunch and no sex, recently he was away on a business trip to the US, and he got her a dress, she of course accepted, however when we checked at home it is very expensive, I asked her to call him and decline/return, but she got angry and said - it cant be returned to the US, to make sure that I dont insist, she cut the label off. (we normally shop at factory outlets or Target/amazon)View attachment 1335405

Any advise on what to do?
Fuck her in the dress. Seems the only appropriate course of actio