Separators between post listing

Hey everyone,

I’ve been working on a portfolio theme for myself and came across a slight problem.

I’m looking to add in separators between posts, but I need the last(third) post in every row to not have the separator. I also need separators between the rows of posts. It can be done using custom fields after each post, but that’s inconvenient, not to mention really sloppy.

Here’s a screenshot to help explain what I’m trying to achieve.

Is there any other way to have the separators appear for only certain posts, and if so, how would I go about accomplishing it?

Any help you guys can offer is much appreciated.

Thanks!

Mark