Complex Drupal setup using Views, Entity/Node Reference and custom content type
You should be able to add a node reference field on the Feedback content type. When your user creates a new Feedback node, they should be able to select the correct Delivery node to associate it with.

You will most likely want to constrain the user's selection options to Delivery nodes associated with that particular user so that User 1 doesn't leave feedback about User 2's delivery. One way to do this is to create a custom autocomplete function and use hook_form_alter() to edit the Delivery node reference field on the Feedback node create/edit form.

On a Delivery node, to display Feedback nodes that are associated with that Delivery node, you can create a View that has shows Feedback nodes that are associated with the currently logged in user and references the current node nid (use contextual filters for both).