Have you check in your relationship logs? There should show all things about him and what you have/haven't done with him. Like this
That's weird, since if Gunnar should not show on your logs, it's mean you have finished the Northcrest event which you should have met Everette so many times. Are you sure that you have found him and Booner? And I have seen some bugs report about Gunnar's relationship log too. I think Hyao will fix it's in the next update.