Current external links editor displays link type as a label or selector next to each link, this implies an external link can only have one relationship. However that's not the case, since we already support adding multiple relationships to a link by pasting it multiple times, but that's not implied in the UI.
To make the whole process more straightforward and clearer, the UI should be optimized to display relationships as a list, in which multiple links with the same URL are grouped together, with relationships displayed as a list below the link. Also it would be nice to have an 'Add another relationship' button for directly ading a new relationship to an existing link. Meanwhile, users should be able to delete relationships separately or delete the whole link with all its relationships.
After all the improvements, the new UI should still support the old approach to add multiple relationships by repetitively pasting the same URL.