I rolled earlier this week with 2 black belts I 'd never met before.
1. First guy I get the lapel stack pass. Once I get the grip, I can normally get the pass 99% of the time. This guy fights for his fucking life for several minutes in it - mind you he is stacked on his neck the entire time. I'm having a hard time getting it too to be fair. At one point I even pass and he manages to get reset in the pass. Afterwards I tell him I've never had anyone counter that pass once I get the lapel grip and he says he was just being stubborn and that I was quicker than he expected.
He could have chosen to just accept the pass instead of hanging out on his neck for several minutes but he didn't. Maybe he didn't want to get passed by a brown belt, let alone a new guy.
2. Second guy I am positionaly dominating the entire time. I get him in an armbar and it is a similar thing to the first guy. He is wriggling this way and that for his life. He finally escapes with a hitchhiker but I honestly thought I was going to break his arm - he just would not tap and was taking risks most people would reserve for a competition.
Once again, he could have chosen to just tap and reset, but maybe he didn't want to be tapped out by the new brown belt guy.
My point being I think it's harder to be humble as you get better. You start having a high opinion of yourself which is hard to shake because its being confirmed every time you roll. I'm guilty of this too - I was a big fish in a small pond. It was one of the reasons why I wanted to move to other schools.
It's easy to be humble when there are large skill gaps - when someone is way worse than you or way better. Where it gets difficult is when you are closer in skill, particularly if they are "supposed" to be a little worse than you, either due to lower rank, less experience, or some other arbitrary metric. I'm guessing this is what happened with you and your friend.
His actions are bizarre, honestly maybe even suspension worthy or something. The truth is he is just too useful an asset to just not roll with not to mention he's your friend. Unless it's a hanging offense, I say talk it over with the guy. Break bread, spin it into a funny memory, and let the good times roll.