Eve you say you would rather let adults make their own choices -the problem is it looks like this woman is not reciprocal to his texts. So she has no choice. You have no idea what is going on and he could be threatening to tell her husband if she does not comply. You must contact her, and if she's not bothered, you are not bothered, and your husband continues -then everyone is on an even playing field., nothing more to be done. Personally I could not cope with that, its a form of being unfaithful, but each to their own, I know everyone is different and I hope you can resolve this.