Why do husbands think online chat is not cheating?

my hsband was online chat with another female, and the content of the conversation was exslisit to say the lest. he clams he was just saying something to her and didn't mean it. but i would never hold a conversation with some of that nature because I AM MARRIED. Needless to say I was very hurt and it has put a ripple in our relationship, because I can't forget what he said to her. and he feels that he did nothing because he never meet her. Though to me how would know if he meet her or not? there fo he has cheated. everything seems to back on track but I still can remember, when he was not so nice.