Creating multiple back links

As site editor managing content with *multiple* "see also" links, I would like each target content to link back to the content I'm updating. The back links should be added without changing the existing links. This is important since it helps visitors find related content, and it lowers the need for manual work from my part.

Required Preparations: 

* A content type with an entity reference field to other content (see attached feature)
* Required modules: Entity reference

Additional Comments: 

* As mentioned in the suggested solution, the back links *are not removed* automatically – which means that if you remove the link on one node and re-save the (previously) linked node, you will get back the first link. To avoid this, you'll need to check which links have been removed, and remove the back links as well. (See screencast for two approaches on how to do this with Rules.)

Modules: 
Additional Resources: 
Solution Video: