I also agree with what the others have said - it will probably lessen with age. Cosby was terrible with Boo but now that Boo is bigger I would say that actually he is more of the bully. However, they don't have a go at each other anymore, they just opt to stay away from each other. So no more fighting (well not often) but def not friends - they seem to have worked out an agreement between the two of them
If Boo gets on the sofa, Cosby would rather get down and sit on the cold floor than let Boo touch him

But then again, he is the victor meldrew of the dog world
Fear not, you are def not the only one with dogs like this