Sometimes the bait is just so darn juicy you can help but bite on!!!
Just out of curiosity - if you two are separated/estranged - why do you even have a joint credit card? The first thing I did when I decided I needed to separate from my AH... get rid of EVERYTHING joint. Joint credit cards, joint checking, hell - I even sent the car I loved and adored down the road... because it had two names on the title. I'm working on getting rid of the house too!! It's all about limiting (the best I can!) my AH's "access" to me.
A joint card gives him a way into your life and business - and it sounds like it's not bringing you peace. Why not get rid of it and get your own individual card - both of you?
P.S. FWIW - if my AH had the audacity to remind ME to pay a damn bill... I would have done more than scream at him.