SB, I read all your old threads a while back. Wow, you have been through a lot and are doing so well. Welcome to the neighborhood! Regarding the party, unless the person throwing the party invited you, I would advise to stay home. Sadly, for many people, losing the former in-laws is one of the casualties of divorce.
"You can't stop the waves, but you can learn to surf." Jon Kabat-Zinn