Why does gillenormand give marius permission to marry in Les Miserables?

Having lost Marius first to the ghost of Marius' father and then to the revolution - it drives him nuts worrying about the boy, which causes him to realize how much he loves him. When he is returned to him he will let him do anything - marry - talk about Republican ideas - whatever. Beyond that, when he sees that Cosette has an extremely large fortune as dowry he figures that it's a good match because she must be of the best upbringing and blood to have so much money.