He invited me over a few weeks ago so the kids could give me a birthday party. They had presents and a cake. Today I'm going over for a holiday activity. I'm assuming H is planning activities for the benefit of the kids, but it still seems unusual.
I believe that is OK. Standard advise it to accept some, but not all invites. I would recommend on declining the next couple.
If you ever need to back out, use this:
"Something important came up. I can't make it to event13" (intentionally be vague)
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712