I'm not going to tell my girlfriend about my recently settled lawsuit
Why wouldn't you tell your girlfriend about that?
She'll want me to buy her something expensive.
Well, there's nothing wrong with sharing. It's wrong to keep secrets if you are in a relationship. She's going to find out eventually.
It's going to be funny when she asks me for money for something.
To me it sounds like you should just come clean and be honest with her.