Roosters, especially cockerels, can get a bit....overenthusiastic. I've heard stories of them trying mating with feet, with corn cobs, with tv remotes.....it's perfectly normal and isn't an issue. If both chickens are happy together, I see no need to separate them. If you see your cockerel become aggressive with your pullet I'd separate them, and if you have issues with overmating, I would get her a saddle. Normally you could just rehome a problem cockerel, but until you can get Sophie some more company you should keep him.