Remember that after the 20, you will taper the final two weeks going into the marathon. You will be rested and psyched in a way that the long run can't simulate. Don't worry about the bad long run, it is a normal part of training. Just be glad you got that run out of the way. It happens to first time marathon runners all too often.
Conversation keeps the mind off the work being done and the company seems worth the extra effort.
Eventually, the pace takes its toll and the time comes to bid farewell as the other runner pulls away. The damage has been done, now the pain starts. It is a tough way to finish a run and your time will reflect it. This same scenario may take place during the group long runs. Ideally you would like to hook up with someone of your exact abilities but this is almost impossible.