These knights are not his friends. Certainly, Tristan respects them - their service to their lord is unimpeachable - but he respects them as colleagues in competition. They are peers, but he doesn't even trust them enough to tell them that they [i]are[/i] peers, because he doesn't feel [i]safe[/i] to be honest with them. 

And, as Nin's made rather clear to him, and Mort has implied, he's right to feel unsafe in honesty. 

He's always retreated to nature, when he's had a crisis of authenticity. It's usually been moments when he's caught himself trying to be someone he isn't. Trying to be interesting to a crush. Trying to downplay his needs and limitations for a mentor. After the performance, he can sometimes feel himself become what he's pretended to be. Not everything that is picked up can be put back down. 

It was fun to play pretend for Mort, with Mort, at Mort. And he's going to need to pretend again, and soon. Maybe for a while. That's fine. It's just important to get [i]everything[/i] out, as difficult as getting all the sand out of a shoe. 

He needs to be alone for a while, to separate the threads of performance from himself. 

Being alone, in nature, is where he finds dishonesty to himself impossible. And maybe, after everything that's happened today, the world still has things to tell him. 

If he can, he'll take two cups of beer from the tavern on the way out, and pay for it how he can.