Advice: coparent pulling away after entering new relationship

I (40F) have 2 kids (22F and 17M). I was 21 when I met my ex and did make some mistakes in straying from the relationship and ultimately was the one to end it. He was understandably upset but has always been a great dad. We did work through alot of the problems and coparent well. We used to do holidays together, family trips, events with the kids, sit together at sports events and were over all friendly.

That is, until he met his current girlfriend. She is 5 years younger and childfree, relatively successful and career focused. Since they met, he has changed. It's like he traded in his family for a single, younger, wealthy version. She has never shown interest in the kids who were 11M and 15F. She tolerates them at best.

He has been less involved with the children since. He pays child support. There wasn't ever a court order because we didn't need it. But now he isn't flexible and isn't putting them first anymore. He won't do anything at all to help me if it isn't something directly for the kids. I'm not allowed to discuss parenting difficulties or anything with him anymore. She gets upset. She didn't even allow him to attend my mother's funeral.

Now there are no longer combined holidays and everything is separate. He won't sit near me or speak to me at the kids sporting events when she is there. Now that my son is about to turn 18, he informed me that we will be no contact. My kids feel he is putting her first and don't like her. Since he moved in with her, they refuse to go to the house to see their dad.

To make matters more difficult, my daughter became pregnant at 19. She is back home and I'm solely helping her raise my grandfaughter. GF said she wasn't dealing with another 18 years of this and they wouldn't be involved with helping my daughter with the baby. It's all on me now.

I’m struggling with how much our family dynamic has shifted and how it’s affecting the kids emotionally. Has anyone dealt with a similar change in co-parenting after an ex entered a new serious relationship? How did you support your children?