Yes this was a serious lapse in judgement, but what about him? You didn't make a commitment to his wife - he did. So yes you were complicit, but he's the one who broke his vows. He's the one who cheated. Let's not forget his culpability. As women we take responsibility for men's actions far too often. Obviously it's good that you are introspective and realizing that you don't want to be in that position ever again, but he's the one who actually cheated.