Corvolin is a material part of the story, but he will not be dateable at least as far as we have planned. We've really been trying to reduce the overall amount of dateables and focus on those that people liked and that we know we can write with confidence on their (back)stories and how their relationship will influence Yarin.
That being said, characters like Corvolin will matter to the story itself, and even though we don't have plans to make them dateable, we may still offer an option to have some naughty side content with them. We didn't decide on these things yet, and will have a better idea when we get to their respective chapters/plot points.