Bad Sibling relationship

What do you do if your sibling that is ten years older than you stopped talking to you, found someone your age, who you guys r not even related to and calls them their new and favorite younger sibling they never had. And your older sibling only graces you with their presence when they need funds to take the “new younger sibling” out (who your still not related too btw). I keep falling for the temporary kindness when they come back into my life I give them cash and they leave again until they need cash again. Miss when I was treated like a younger sibling and not a cash cow . Also this has been going on for three years plz how do I grow a spine