My 4 years old pup have not eaten for about 4 days. He has taken a few (and I mean, few) bites from my hand but he refuses anymore than that. He has always being very finicky and the vet keeps telling me that when he gets hungry he will eat.
Well, is not working... Whats concerning me is, that if I give him snacks, he will eat 4,5,6 pieces of them.
I adore this dog and I cannot imagine what my life will be without him.

If the vet isn't concerned, likely the problem isn't critical. Read through the sticky at https://www.askmehelpdesk.com/dogs/information-articles-our-dogs-expert-labman-53153.html#post254171 Pay particular attention to the link on evaluating your dog's body condition, and the discussion of overweight shortening dog's lives.