Dogs are pack animals, meaning they are meant to be socialized, but provided human interaction is sufficient, they do not need to be kept in pairs. Try to spend as much time as you can with your dog to see if that helps.
Whether or not dogs should be kept in pairs depends on the individual dog. If your dog enjoys playing with other dogs, and you work away from home so the dog is often alone, you may want to consider a second dog.
Some dogs require companionship and are apear to be lonely. There are, however, many dogs who are very happy alone and tend to be very jealous when there is another.
I think no. You just can find someone, that has the same dog, and meet him/her everyday. If your dog seems lonely, play with him, maybe You should visit vet.
