Despite you were a new disciple of the Order of Shadows, he had his eyes on you from the first time you put a foot in there. So, the fact that you trained with other people, that you interacted with other people, even if it was Master Zed, made him see red. It filled him with an anger that, the more time passed, the less he controlled it.

And it only grew as the days went by.

So when you go to him to ask him to train you, he doesn't hesitate to take it out. After all, is your fault he's feeling like that, isn't it?

He, having much more experience and, in addition, being good at all the weapons, does not hesitate to let his rage out, being relentless and ruthless with you.

And you didn't realize his emotional state until Kayn had you under him, pinned, and you got to see how mad he was just by looking at his eyes.