Count how many conversations users have logged with other employees

Without some custom script, it is not possible to evaluate other records that are conditional on items being entered in a form.  Especially with so many variables.  (Dates, resource 1, resource 2) and if those variables are in different orders.

If you are looking to keep it as 'native QB' as possible, I'd recommend handling this with well designed embedded reports that show existing logs, and connections.  Thus allowing the user easy visibility to the previous logs.