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I vote for you getting tested before you break up with him (and I think you should absolutely get tested ASAP). If you get good news, I vote for not telling the wife. My guess is that at some level, she already knows. If you do test for a disease, then you should tell his wife because you have good reason to contact her. However, I think it's really important that you look at what your intention is to contact her, if you test negative.
My other suggestion is that you engage in some compassionate self-reflection as to why you got involved with a married man in the first place. Good luck to you.