Ari became the School's main Eraser mostly because of his father, and after all the experiments put upon him, literally went crazy. He blamed Max for all his problems, and resented his father, Jeb.
Max killed Ari in a sewer when he attacked and tried to kill her.
He was later resurrected, only to die later from the intense mutations the School preformed on him.
When he and Max find out they are brother and sister they feel a minimal connection, though Max is racked with guilt when she kills Ari and is sad when he dies.