Here is a solution using the Entity Reference module to display other nodes that reference the same node that the current node references. No need for relationships, just follow these steps:
- Make sure you're filtering the view by the content type you want to view a list of, not the one you're trying to reference.
- Add a contextual filter using the entity reference field.
- For the entity reference field, choose to provide a default value in PHP ¹.
Adapt the following code to your field names ² and save the contextual filter:
$node = menu_get_object();
$referenced_node = $node->field_YOUR_FIELD_NAME['und']['target_id'];
Save the view and check it out.
¹Disclaimer: PHP should never be used in the UI due to concerns with security, performance, & lack of version control. As a result, the proper way to implement this solution involves writing your own simple module that creates a block that passes the argument into the view as you render it in the block. I'm still including this because whether people ignore this warning or use it to write a module, hopefully it helped.
EDIT: If you also want to exclude the current node, you'll need to add an additional contextual filter for NID and make sure to select the "exclude" option.
² Not sure what your field names are? Install and enable the Devel module and visit a node. Click the 'devel' tab and navigate through the list to find your desired entity reference field.