hmmm... tough question, haven't given it much thought really since it hasn't happen to me( i mean my partner having a kabit). But i'll probably do nothing and go about my business, since in the first place I probably would have left my partner the moment i learned of her infidelity. So even if we met no use really to confront the kabit since it’s all over anyway.
To me i don't think it would still work if one cheats since the trust won't be there anymore, and her/his infidelity will just cause problems in the future especially when u have fights there's a good chance you will bring it up. So it makes a lot more sense to separate, but like most things it's easier said than done especially if u have kids.