I honestly blame both of them for how toxic their relationship became.
But you gotta admit, it's mostly the FL's fault for lying all the da** time while the guy keeps saying he loves her and even wants to marry her.
Lying she'll marry him and lying about having some other guy's baby. Of course the guy's gonna go crazy but yes it doesn't justify what he did. He went too far with the fire knowing that it could trigger her trauma too like come oooooon