it is toxic but it ends well for the MC because his love and sincerity towards the ML is pure and very assertive. So much that ML spares him from being killed, changes his own name to show he is the wife, and guards his purity about the world. He is justified in his revenge against people, but only MC was innocent; he was going to kill him as collateral, but decided against it. ML still goes through with his revenge on everyone but they become a good couple!!!
Ok spoilers i wrote before
https://www.mangago.me/home/mangatopic/21678538/

Do they end up together? So many people said the novel was dark,so I'm kinda scared