Leonce Pontellier has never seen himself as a victim of any kind of behavior coming from Edna, or anyone connected to her. His only aim in life is preserving appearances, and prolonging the illusion of success in every aspect of his life.
When Robert left for Mexico it came as a surprise to Edna and it clearly affected her behavior. Whatever Leonce Pontellier felt as a result of the news of Robert's departure must have struck them as an advantageous opportunity for financial success. Therefore, if Leonce Pontellier express sympathy towards Robert's departure it was because he genuinely felt that it would be a good chance for someone to make a good living.
Regarding Edna, however, Leonce would not have even noticed any difference in her demeanor. If he did, it would have gone straight over his head. She was not his priority: He was his own priority. Hence, Leonce (in his capacity as a businessman) would have heartily agreed that Robert's best chance was to try his luck somewhere new.