For what I get from your mockups, I think your problem is the lists are not connected, but the elements inside those lists may (or may NOT) connect to another element, thus lists are hard to connect. If you take a closer look, you're trying to connect elements from left list to resources that may fit into the following statuses:
- true the activity contains resource X
- false the activity doesn't contains resource X (but contains another resource)
- empty the activity doesn't contain any resource
Similarly, the following happens with the right list, with same logic:
- true the resource belongs to Activity X
- false the resource doesn't belongs to Activity X (but belongs to another activity)
- empty the resource doesn't belong to any Activity
Therefore, my suggestion would be to simply get rid of the right column, and show sub-sets of an element inside its appropriate set. For this, I'd use an accordion:
Just in case it's not clear from the mockup, the resources displayed are ONLY THE ONES THAT BELONG TO THE ACTIVITY, and nothing else. There's no point in displaying null sub-sets, it just adds noise to the communication.
Now, if you still want to show those resources lists, you can add then in a clearly isolated block element that has absolutely no relation with the activity list. And once an user click on a resource, you can send the user to another page or open a modal and display the activities this resource belongs to.
Hope that helps!