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.
Brom was friendzoned, and he never made any moves on Katerina. Even then, it wasn't about saving the realm, but the tragedy in losing one's husband to-be at the hands of a traitor.
Don't worry about it though, I'll just go poison Allison and watch you jump off a balcony
.