Jason left Sable because either 1. Sable railed so much against Jeff and against Connie's stock transfer decision and/or 2. Sable tried to gaslight Connie and/or 3. Jason wanted Frankie all these years ago, and Sable was his consolation prize and/or 4. He wanted someone equally boring by his side but looks weren't really a reason. I mean, the man looked like he was due to be embalmed (hey, good solution to his fake terminal illness).