Re: How to deal with my situation?
I would say the first option. He's trying to get a rise out of you, even if it's negative. It's a roundabout way of trying to justify why he left to himself, to say "See? This is exactly why I had to cheat and yadda yadda". After all, you're the glue/"enemy" that's holding their relationship together, and without you where would that leave them?
Continue as you are and keep regarding them in a business-like and professional manner. Like gum on the bottom of your stilettos. Keep documenting his vitriol. Truly happy people don't try to keep bashing their exes to their faces while claiming that they're happy.