I think my SO is turning into an extreme cheapskate

He's always been cheap and since being with him over the years I've become careful and thoughtful with money. We both just like to save. Anyway I bought a disposable (cost $1.50) cardboard cupcake box bc I'm making cupcakes for my church. Tonight he asked me if I can wait after church until the bake sale is over to collect my disposable box. I thought he was joking but he was serious. How can I stop him from being so cheap!