Sil is having her son's first birthday party on Easter around lunchtime. it will be his second birthday party, not counting the celebration on his actual birthday.

we already have issues (the sister and I) because she lies constantly and steals things from my son, who is a few months older than hers. She's nice to my face but goes and tells my evil mil EVERYTHING

am I wrong for wanting to keep this day as family time for my son and I and not wanting to go to her son's second party? I'm weird about holidays and don't really consider sitting uncomfortably in a room full of judgmental people 'family time'

How do I tell my SO I don't want to go without upsetting him