I got your point: the line in the SQL diagram, when you click “Add Related Tables,” and based on the key relation, it loads all tables in the diagram.
As I know, it is not available here. But I think it would require extra coding to use this feature, and as I used ERwin, Lucid, etc., no one has these types of features. As far as SQL Server Diagram, that is not an ER model; it is physically relationship among tables that is converted into a diagram to display.
Let us know your comments on this.
Thanks,