One thing jumps out at me with this post. First is you got your male dog a male puppy! I don't know about other breeds but this is usually not a good mix with Goldens! Especially if the puppy displays dominant traits.

Another thing that may be going on is the dog is now insecure because of your attention to the pup. I have a 3 1/2 year old female and a 5 month old pup (who is the son of my female) and she was starting to exibit signs of depression at his being around! What you need to do is show the dog he is still the number one in your heart. You need to talk to him first, feed him first, pet him first, let him out first, etc.... everything has to be him first! This is not unfair like it would be for human children. Dogs are pack animals and need to know the pack heirarcy.

Feed him special foods for now to get him eating again. Forget the dog food for a few days! Hamburger and rice is a good one to get his appetite going again. Give him Steak, Liver, Chicken, Cheese, anything he will eat. Hand feed him if you have to and do it without the pup around.

This situation is unfortunate but it can be turned around. I know you are probably thinking that this will be unfair to the pup! You are still going to show the pup you care but you need to let him know that the older dog is the higher ranking dog in the pack. Once the older dog feels less threatened by the pup then you will see his behaviour improve dramatically.

Best of Luck in solving this difficult situation. Keep us informed how it is going!