I don't know whether it is a "criminal assault" or whether she seduced him/ took advantage of him/ etc. it seems that he didn't initiate this and the problem is just that he allowed it to happen, i.e. he didn't object enough. partly because (if we accept his story at face value) he was taken by surprise.
but what was, was. the question now is: was this a one-time mistake and is he taking steps to make sure that it doesn't happen again? has he made it clear to this woman that he wants nothing more to do with her? there are additional things that each of you can do to make sure this does not happen again - and that is what is important. we cannot change the past, but we can change the present and the future.
again, see specific recommendations in "Not Just Friends" and "Divorce Remedy".
