Create related nodes to specific node I am using Drupal 7.

In one of my requirements i need to create related node to specific node.

For ex. I have created a node of content type "article". For particular node of "article" node 

say nid:9 then i would like to add related node to this node.

So when i view nid:9 at that time it should also display related nodes, and also when i view the newly created node, at that time nid:9 should be displayed in related node display

So both nodes should be displayed vice versa in each others detail view.
There's quite a few modules that relate two (or more) nodes together, Entity Reference and Relation are both popular.

I'd probably recommend the Entity Reference module as that comes with a couple of field formatters that display the referenced entity. If you used the Relation module you'd probably have to build a fairly complex view with contextual filters and relationships - this screencast series should help with that.