For the divorcees: how do you tolerate the ex wife?

When I first met my husband, 5 years ago he had extreme hatred for his ex-wife. I tried to be very open minded and give his ex the benefit of the doubt on many things because there are kids involved. I knew if this relationship was to develop into more, which it did, that she would always be in the picture or at least until the children are grown. Five years later I have grown to hate her and he is just ambivalent. He could care less what she does are says which is a sign that he is emotionally over her (when I first met him I think he was still stinging from the pain of the divorce). On the other hand, I find the her actions and cutting comments drive me insane! My husband and I have almost switched roles in terms of feelings for her. Bottom line, I want what's best for the kids and I don't want them to know I really, really, really, dislike their mother. How do I put a smile on my face when I see her and treat her with professional courtesy? I would like to avoid her, but there are way too many social interactions together (i.e. kids' games, school activities, etc.). Suggestions from any of the other second wives out there?