Controlling access to nodes by simple user relationships

I looking for solution or ideas about how to solve this problem in Drupal 7.

I am going to have a site where users will be working in pairs. One user(Poster) will be posting nodes and another user(Viewer) should have View access to posters nodes. Nobody else outside of these 2 users should be able View the the Posters nodes.

I have thought using the User Relationship module, but it seems overly complicated for what I am trying and would present other problems for my purposes.

I have thought about solving this problem with custom code and the ACL module.
Here is my idea for that:

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I am not sure if this is a bad idea to have list for each user with the Role Poster(half the users on the site).

Any ideas?

Thanks