vent-my dad excluded me (18f) from little brother's (7m) bday

my dad has a new family, i wanted to go out with them to a restaurant to celebrate my (half) brothers bday like they usually do, but this time he didnt even tell me and by the time i asked him to come over he told me they were already out. and this isnt the first time something like this has happened, he didnt invite me over on eid but invited other family members and made excuses to why he couldnt invite me. and his wife hates me and tells her kids (My siblings) terrible things about me which makes them not want to talk to me (except for my brother who sticks up for me and sees through her bs). im just tired. i was already sad today and this ruined my day even more.