What kind of idiot would send a Christmas card addressed to your W and New Guy to YOUR house?!
I don't know what to tell you. If you have been too nice and you think that could have been a factor in the demise of your marriage, then why NOT stick up for yourself. It would be a 180. I know that my H liked it when I would get sassy and stick up for myself. Of course, if I did something like that now, I don't think he would "care" either way. And maybe your W wouldn't "care" either, but you would be able to look in the mirror and know that you didn't just turn a blind eye.
Hopefully expert DB'ers will chime in.
Me-43 H-46 M 12 yrs 7/09 T 15 2 grown kids bomb 7/05/07 H moved out 8/04/07 11/22/09 told him I quit;let's get ball rolling Mid Dec- he isn't sure he wants D End 2/2010-Starting to consider piecing