Why is jean val-jean despondent after cosettes wedding?

Jean Valjean is despondent after Cosette's wedding because he feels like he is losing her to Marius, who is now her husband. He also realizes that he is growing older and that his presence in Cosette's life will soon diminish as she starts her new life with Marius. Additionally, he struggles with the idea that he may no longer be needed or have a purpose now that Cosette has someone else to take care of her.