This story was very dissappointing. I felt whiplash going into the back story -- not even an attempt to describe some segue, just HEY, WE'RE IN BACK STORY NOW!!!
Plus, I expected the dog to be metaphor, like Tell Tale Heart -- some expression of guilt the MC felt subconsciously. But nope -- it's real and it's...well...can't be killed, but...it left him alone after it got shot because...well...
I could buy that the dog would leave him alone if there had been some change in the MC, but he didn't change. He just got caught. So, why did the dog leave?
I think theme, plot, pacing and metaphor got splattered in this one. A good tale on its face -- cheating husband gets stalked by sinister black dog -- but there was no attempt to wrap it all together either thematically or plot-wise.