He punches Eren in the face, asking him if he actually believes that telling Mikasa to forget him will make up for the way he treated her the last time they spoke.
Thank you for dedicating your heart, Isayama! Rather than say, the centipede acting like a genetically carried disease, or mutating Eldians -- the more scientific explanation -- the Titan curse is literally a curse.
Armin jokes that Mikasa will easily find someone else to replace Eren, causing him to break down and admit that he does not want Mikasa to have feelings for anyone other than him.