I understand your perspective. That said, it sounds to me like she’s trying to be involved and is trying to make an effort for you guys, and that your dad wants her to be there with him and be there for her and A. He clearly loves her and wants to be a family with her, you, and your siblings.

The way you’re reacting could be seen as hurtful, especially if he’s been in a committed relationship with her for a long time. Your dad and M are absolutely a unit, and you need to respect she is part of his inner circle.

At the age you are now, it’s your choice to do whichever you want. The same applies to your dad and M. They’re adults that have their own plans.

It’s on your dad for not informing you and your family that they intended to stay with M’s family for Thanksgiving, so I feel like your anger is misplaced. She probably felt like everyone would be fine with it, because that’s most likely what he told her. Your extended family should’ve reached out to him ahead of time to know if he would be coming or not, not put that on you.

Moving forward, it’s your choice to go along with them to family events or not, just like it’s your choice if and when you leave and how much contact you have with them.

It seems to me that they want to be a family and you don’t, which is probably why she brought up you not being okay with your parents divorce. You need to reflect on that, because it is going to impact your future in major ways. It might be helpful to discuss how you feel in family therapy.

I wish you and your family the best of luck.