I really liked this and I'm often referred to as dead inside.
The characters were spot on, the relationship was on the money and in no way creepy (which I have seen in an old man, young person piece on here).
Harvey come across brilliantly, he's bright and caring but in an understated way which is great. I find his endeavours touching but I do feel that the old man could offer more.
Could there be more to his story than his lost loved one? Could there be something that haunts him from his past that he must overcome before he can let Harvey into his life.
He welcomes Harvey a little too easily, could you make it a little harder for Harvey, the old man is complex and needs some thought-through care if Harvey is going to achieve his goal of making him happier.
Like I said, I haven't really dabbled too much in this kind of writing so I might be way off the mark but I would like to see a dark secret in Soulby's past.