ANSWER:
I don't think it's smart to talk to this other woman who had the affair with your husband. I know if you do, it will give you some closure on why he cheated on you. You will not learn anything useful. Even if she was gracious or friendly and give you all the tiny details about your husband, how would that help you? This mistress doesn't owe you nothing, even if she was the party to your husband's infidelity but he is the one who cheated on you not the other woman. Your husband made the vows of fidelity to you, not his mistress. He brought her into your marriage and put you in this situation
You will not gain anything if you choose to talk to her, so if I were you I wouldn't. I am not supporting the mistress in any case, but I was in your shoes before and take my words for it, even she didn't say no to my husband, it was him who started the relationship.
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You could ask her directly about her involvement with your husband and confront her about her actions. It may also be important to ask about her intentions and seek clarity on the situation before deciding on how to move forward.