Nathan hadn't been expecting that reaction from Peter, or more accurately hadn't been clearly thinking about the result of actually being upset at Peter rather than controlling his feelings as he had been lately, not wanting to press in or overwhelm his brother. Peter had enough to deal with inside himself without taking on the emotional burdens of others. It was the first burst of free emotion in many days and he intensely regretted it. Whether he thought Peter leaving had been a stupid idea or not, whether anyone else understood what had happened recently here or not, he should have known better, he should have kept in control.
It was easy to remember how to hate oneself with so much fodder for the feeling.
The apology was on his lips, but wasn't uttered because Annie's entrance distracted him, rattling and banging and all. This was really not someone he wanted to upset further, not just because she had the power to rip his head off, but because he liked her.
And then glass and wood shattered and Nathan very quickly put the the 'head ripping power' over the fact he had upset someone he like and realized it was time to bow out now. He couldn't risk Annie not understanding his explanation of his behavior. And he could clearly see Annie wasn't the only one of that opinion.
Annie, Hiro and he himself made three. Bad brother indeed.
And then another person joined the fray. Nathan didn't know him, but he wasn't a fool and could see he was very much outnumbered.
"Pete. I'm sorry-" he said quietly, even as he backed slowly away. It had every appearance of someone not wanting to aggravate something dangerous.