Most Helpful Guy
I think its because he felt guilty about ruining the marriage. So he let her stay with him, now she is replacing her husband with him, and he is just letting things go forward.
Him contacting you? Personally I think your best friend might be less than stellar. I would not, and will not be friends with someone who would go into a relationship with a married person. There is no honor or dignity in that.
He is justifying what he was doing with the married chick and he seems to think that he is ok with his choices. Does the married chick know he is still talking to you?