Married couples separate/divorce for all manner of reasons, but it isn't often due to hate. Your girlfriend seems to be qualifying your relationship with your ex wife based on her own experiences with her ex husband.

You have a history with you ex wife that cannot be erased, you are still raising children together, and both seem to be making a good job of this. Your current partner needs to take a step back and appreciate that it isn't a competition, you are with her not your ex.

The Thanksgiving dinner is a no brainer....we congregate with family and friends to give thanks. Whether your girlfriend agrees or not, your ex wife is both a friend & family. Thanksgiving also isn't a competition.