Whos party should i go to?

Okay so my dad and mom are divorced and tomarow i am going to my dad's cousins fourth of july party, but my boy friend asked me today if i wanted to come to his tomarow. i know it would be wrong to go to my boy friends party since i already said id go to my dad's but the thing is my dad has never been there for my brother and i and he always cancels on us. mostly he chooses paartying over his kids :/ and for some reason i feel bad about ditching my dad but in a way it seems unfair to have to go to a party where i wont know anyone vs. a party with someone i like and his family which is really nice. so what do u guys think? thank you :) im just so confused and conflicted