NIDOME NO JINSEI WA KOUKAISHIMASEN: KOUFUKU END WA FUKUSHUU NO NOCHI DE

Ceriniel is heartbroken when she learns her husband has been cheating on her with her best friend and secretly poisoning her for years. But when she dies and wakes up in the past, she's determined to get revenge on those who betrayed her. And so she bravely seeks the help of the bloodthirsty war hero, Duke Lexion Rosenvester, who was oddly kind to her in her past life. His only conditions are that she ditch her unfaithful husband and enter a permanent marriage with him instead...!

(Source: Tappytoon)