I truley believe dogs can and do mourn. Looks like this guy is distressed and mourning for his buddy
I had a pair of Japanese Chins..unrelated, male and female. They loved each other, had kids..went everywhere together. The female was a bit older than the male and after several years she began slowing down. She became real listless one day, wouldn't eat, drink, play...just wanted to sleep...so took her to the vet and they couldn't find anything wrong and said just watch her. A morning or 2 later I woke up and found her laying in a little ball barely breathing, real cold...and the male cuddled up next to her. It was really early in the morning and the local vet wasn't open yet so I covered her and put a heating pad to keep her warm....the male always with her. Probably an hour later she passed away, quietly, peacefully...I was devastated...but didn't realize how it effected the male. He flipped when I put her in a box and we had to put him in the bedroom when we buried her in the back yard. He looked and looked for her for hours, crying...frantic. A day or 2 later he too got real listless....took him to the vet....again, nothing physical was found despite having many tests run. He passed away 4 days after the female, and I had the vet do an necropsy (sp) on him to be sure they hadn't died of some hidden disease. The vets conclussion? She had died of old age.....he had died of a broken heart. So yeah.....don't tell me animals can't mourn.