How can i require customers to buy both products in a bundle?

The best way to achieve this is simply to create a classic bundle. To create a classic bundle, go into Bundler > click the “Create bundle” button > select “Classic bundle.” 

Then, scroll down to the “Discounted products in bundle” section and add both of your products in there. 

Once you configure the rest of the bundle (e.g. discount, etc.) simply save the bundle and that's it.