You could do it, but I just don't think it would do any good. The OP that gets involved with a married person with kids don't put much respect on morals or values or marriage. If he had a W, then maybe that would do something, the fear of getting caught, but you said he isn't.
Only benefit I see is IF Bill's W did not tell OM she was M'd (sorry if I missed that part) and the OM happens to have any moral fiber. But, if OM knew this, and was interested in becoming involved, he has no respect for a family anyway. Even then, maybe this guy's a coward and may run once confronted.
In any case, it is not worth devoting a lot of energy to. Face it, and move forward.
