I don't want to help my boyfriend
Why? Did he do something that upset you?
Yes, I don't appreciate him buying the cake.
I am not sure why you are upset about cake but it is wrong for a girlfriend to not help her boyfriend when he needs something. You will be seen as selfish.
It's okay to help him, but he is going to fail the test. So why help him?
You help because it is the nice thing to do. You should help him when he needs it.