I thought we might have a brief discussion here regarding your latest owl. Miss St. Clare has much to recommend her, not least of which is her apparent disregard for the custom of monogamy. Keep in mind that you do not plan to be monogamous. Or not with her. She is therefore likely to be accepting of your relationship with Severus, as well as unlikely to make a match with prospects who would be your competitors. She is attractive, well-off, and her family has much to offer.
Regarding your demands as to her behavior, it is a bit much to expect that a girl with her nature will agree to abstain from carnal activities for twelve years, until the child is of school age. While I think it not unreasonable to demand that she dress appropriately, and that she conduct her affairs with the utmost discretion, I urge you to consider this an article in her favor rather than the opposite.