I 100% agree with Ginger’s advice. Any invites like this should come from your XW. I have made a point of requiring XH to be the person communicating with me regarding our children. Not just because it is his responsibility but also because it is important our kids see us as united in our efforts to parent them. Both XH and I have made a concerted effort to be reasonable and cooperative with one another and it can only benefit our kids in the long run. I also agree that ignoring the invite is a reaction and just paints you in a negative light (even though no one could blame you for feeling that way).
I completely understand your feelings BL. XH was dragging our kids to OW’s family events before I even knew she definitively was OW. And now they are married and he (mostly) lets me know when my kids are involved with her family. For instance, my daughter and her bestie went and stayed at the lake with OW’s mom for a couple days in the summer and he texted me to let me know. Was that a bit of a trigger? For about ten seconds and then I looked on the bright side… my kids have a stepmother whose family cares about and includes my children in their lives. I would have way more concerns if it was the opposite because then I would have to worry about my children’s feelings. Currently, the only feelings I usually have to worry about are my own and those get less and less intense as time goes on. If this had occurred this time last year, instead of ten seconds, it would have been a couple hours of negative feelings so distance and time does help. In the future, I fully expect it to be a non-issue. Now my kids are 13 so it is not exactly the same situation but the principle remains. You may not get to choose what happens to you but you do get to choose how to respond to it. As always, choose better not bitter. If you can do this consistently, long after the hurt feelings have faded away, you will look back on this time and be very glad you did. (((HUGS)))