IMO, this young man was too depressed to deal with life's challenges, whatever they might have been. It can be impossible for a depressed person to come up with and carry out a workable solution to a problem -- it's all just too difficult and complicated in that state of mind. I'd love to blame the condo board (hate them!) or his neighbors for his suicide or for his euthanizing his dog, but I just can't.
For context here, I own a wonderful pit bull whom I love more than life and have often experienced the negativity of "breedists." However, I don't think the condo's new rules were unreasonable. Pit bulls are commonly dog aggressive, and might attack other dogs who are present when elevator doors open. I also don't think it's unreasonable to insist that dogs not be left alone more than 9 hours.
There were many solutions available to him. He could have kept his dog and moved, kept his dog and stayed, or found a different home for his dog. If he were really poor and struggling financially, he would not have been able to afford to live at One Lincoln Plaza (starting at over $800,000.00.) Pit bulls are very popular dogs and are not routinely put down by the Humane Society in New York, so taking his pup to the pound or advertising his availability was one option some people might take.
I feel terrible that he was so ill that handling the difficulties of life was impossible for him.