I don't think he will have too much trouble finding a wife of quality. He is rich, he is to inherit a title, and the double standard was huge then. The more fastidious might turn up their noses at him, but from all I've read, it was fairly common for rich men to sponsor a mistress.

He won't have much trouble marrying well - but Mrs Clay is now beyond redemption. She has put all of her eggs into his basket, as it were, and if she doesn't succeed, when he eventually throws her over, her only choice is to move on to another man, much like poor Eliza in S&S. It is a huge risk she's taking, and I doubt she'll succeed.