"As for Clarisse, she was charmed upon receiving her husband's letter. She and the babies were doing well. The society was agreeable; many of her old friends and acquaintances were at the bay. And the first free breath since her marriage seemed to restore the pleasant liberty of her maiden days. Devoted as she was to her husband, their intimate conjugal life was something which she was more than willing to forego for a while."
Alcee did not send this letter because he was unselfish. He sent it because Calixta had just satisfied him. She never knew about what happened between him and Calixta though which is why she is rather pleased by the letter. Just like Alcee, Calixta is happy in the end because her family comes back home safely and her husband or son did not come home while Alcee was still at the house.