What do you think about me not going to my boyfriend's sister's birthday dinner?
Why wont you attend the birthday dinner.
I do not care for his sister.
You should attend event you are invited to. It would be good for your boyfriend if you go to show support.
If the people he cares about don't show up, then it means he doesn't care for them. Well, his family isn't any different, but I agreed to attend in the first place.
Well, if this means that you're going then that's great. You should always show up at parties that you're invited to, even if only for a few hours just to show support for your boyfriend.