I've linked Cases with custom object using lookup relationship.
However the custom object page layout is missing the related list.
What am I missing?
[SalesForce] Related list is missing from page layout
Related Solutions
The checkmarks for “Related Lists” on the mini page layout only affects the display of a record in a Console view.
From the Salesforce Help:
Related lists on mini page layouts only display in the Console tab, not hover details.
For example, if you set the Top Sidebar Custom Console Component for the Case Layout to be a Lookup to the Account, you’ll see the related Account record in the top panel of the Console along with the related lists that you checked on the Account’s mini page layout set up.
Here's the result of a Case Console Component of the Account lookup in the Top Sidebar with the Account's mini page layout specifying that the Notes & Attachments related list should be displayed.
Since the lookup is from Partner to Contact, you'll see only fields on the "child" side of the relationship. If you go to Setup > Customize > Contacts > Page Layouts, you can add both related lists (Billing Partners and Business Partners, or whatever you called them) to your contacts' related list section. From your example, Y.Foreign_Key = X.Primary_Key, Y.Foreign_Key appears a field on Y, but appears as a child relationship (related list) on X.
Best Answer
You named the Related List Label "Supplier Relations Escalation", so that is what it is called on the Page Layout. You can see it on the far right of your options.