Shouldn't have poisoned Katerina's husband you scoundrel - you were her best-friend, and you deserved to watch her die! 
Katerina should have seen Brom was a much better option. On the other hand, I gave him the antidote and he wasn't doing that great being King anyway. The realm could have easily been saved with Katerina not jumping out a window.
On the other hand, I would have never done it if I'd known they were engaged. Was really left without any options past a certain point though.
