I feel like I don't want to go to my cousin's baby shower.
Why don't you want to go to your cousin's baby shower?
Because I hate the fact that he knows more about my family than I do.
It's good to support your family, but if you don't want to then you have no real obligation to do so. Just make sure you don't tell them you're going and then take it back later, as that would annoy most people.
I'm an only child, I don't see why I have to be at these things.
Your family might really want you to be there, and it can be a very good thing to support your family.