The more specific one's training becomes the harder it is to run with someone else.
Firstly you must determine "WHEN" the run will take place. This can take a miracle to actually match up a day and time when both of you are available. Then the "WHERE", "WHAT" and "HOW" must be determined. What pace should you run at, what distance, a long flat single track, a short steep uphill climb, etc. etc.? Add a few more people into the mix who are recovering or tapering or have injuries to consider and it can all get rather complicated. All the variables MUST be considered and accounted for before the RUNNING DATE can finally be consumated.
P.S. I hope you get this one because it took most of my brain cells