As far as OM - same with my kids. He was the "fun guy" while XW let them do what they wanted - while I continued parenting. He bought them toys, and let them eat donuts for dinner, all that stuff. Don't sweat it. Kids don't know what's going on except they get cool fun stuff.
Secondly, you were fine to ask for the debit card. Don't respond. Remember the goal is to make you look bad in any possible way for anything you do. Maybe next time leave off the "before you spend anymore" comment.
Finally, your W is almost completely in a relationship with another man. She is consistently using you; the debit card being the latest example. That was "not an accident". Why would you invite someone like that to your house for Christmas?
