Well, I guess you know what my opinion is with 14 dogs :wink:. But seriously, I really think that if you got another one, both dogs would benefit. I agree with everything that has been said by others. Even if I were not breeding, I would never have any less than 2.
One thing that I would add if you decide to get a puppy. I know some breeders will disagree with me, but we have had good success with having the puppy people bring their Cavalier (we only do this with Cavaliers and with other conditions) when they come to visit their new puppy. The people's puppy and Cavalier may not get along real well, but it will give the Cavalier a chance to smell the puppy and possibly remember the puppy when it's brought into the new home. We have tried this as an experiment 3 or 4 times and the people said the get-aquainted period when the puppy came home was very short. This is definately something you would have to clear with your breeder first. And don't be offended if they don't want to.