AITA for Keeping My Stepson’s College Fund After He Helped His Mom Hide Her Affair?

I raised my stepson from the time he was five years old and spent years putting money aside so he would never have to worry about paying for college. Then I discovered my wife was having an affair—and started realizing her son may have known more about it than I ever imagined. I filed for divorce, walked away from the entire family, and kept every dollar of the college fund I had spent years building. At the time, I was certain I had every right to. Years later, one unexpected encounter made me question whether I punished the wrong person for what happened to my marriage. AITA for keeping my former stepson’s college fund after discovering he helped his mother hide her affair?