usually the case is that the wife kicks the valet out, and he rather enjoys the posish he is in now.

True.

I think, setting slash aside, the most probable reason he doesn't want Bertie married is that he'd lose his complete control of his meal ticket. The only way he'd let Bertie get married was if he could find a fluffhead of a girl who was just as happy to let Jeeves run her life, and she didn't want children.