Cocker Spaniel Behavior ?

If you have been to our website, tobyzwebsite.com, you know Toby's story, so I always thought that Toby howls when he is away from us because of his abandoment issues, but I have been told by other Cocker Spaniel owners that their dogs do the same. Previously I had a Cocker Spaniel from the time he was a puppy, and naturally he cried when he was first put outside at night, which resulted in his becoming an indoor dog. Shortly after getting him we got another dog and they were always together. I never remember his howling; I have to wonder is it because he had another dog to keep him company? I have thought about getting another dog, but Toby seems to require a great deal of attention, and I am concerned that he would be hurt if another dog was introduced. When he has been around other dogs, he interacts with them until he is bored with them and then turns his back and leaves them, even if they still want to play. Are his lack of social skills the result of his not being brought up around another dog on a regular basis? Is his howling when left unattended even for few mins, when dropped off for grooming, or when taken doggie day care normal?