I am definitely not letting the guy off the hook. Thank you for further explanation. I feel bad for people in these types of relationships because they rarely end well. When I say exposing the wife, I am talking about potentially. Unless you use protection you are also exposing yourself to a guy who has already being dishonest with one woman. Even though the wife does not know it, she is still being made a fool of and I just cannot go along with it being all right.
The guy you were with would likely not consider you anymore than he has considered her. My only thing for you is to say, I believe you made an unwise choice, but I do not judge it. I have been in a long term marriage where that has not been a problem, I was also married in my youth and that did not work out because neither of us were really prepared for that sort of commitment. Both of us ended up wanting other people in the general sense.
I wish you the best with love and no judgement.