Heroine kills hero for greater good trope name?

Spoiler warning for "the great".

You know the part in "the great" where Catherine finally starts to overthrow Peter and he says if you don't stop I'm killing leo and velamentof says do it so she goes out to the forest to say goodbye before re-starting the overthrowing and therefore killing him. Yeah that. What's that trope. I need my heart to be broken in 40 pages on a 2 minute segment.

And if anyone has recommendations based on that scene. That would be great.