For those wondering whether the starfish was harming him with its actions or not, here's my interpretation:
The starfish is an emotional leech. Just as a leech has an anti-clotting agent to keep the blood from scabbing over and blocking the wound, so does the starfish have an effect that causes its subject from healing and thus keeps its food source flowing.
So, instead of grieving, and allowing himself to heal, this creature keeps the wound open until its ready to move on to the next host. How could you grieve a woman who you feel by your side every day? It's parasitism is of a unique nature that the host, because of the nature of his grief, does not WANT the wound to heal. It's sad to think that we could possibly ever be "over" the death of a spouse, so we want to keep them close to us always, but it's not emotionally healthy to do so. I got the impression the old guy had been in this emotional limbo for decades, never able to move forward with his life. That's where the horror in it was for me.
I liked the story overall, but there were a couple parts that didn't seem to mesh with the rest of the story explanation:
-The old guy disappearing spontaneously.
-The ticket at the end. Why does the starfish need the ticket to do its work?
Also, I was excited at the beginning of the story to see a Minnesota setting. I live in Minnesota, you see, and it's refreshing to see a setting I'm familiar with. Not only that, I am taking grad school classes at the U of M Computer Science department, which shares some classrooms with the math department.
But the setting was so over-archingly generic, that the mention of Minnesota could have been any state that has a college, and winter weather, so I was quite disappointed. The only other local information was the name of his hometown "New Ulm", but anybody could've grabbed that off a map. It wouldn't have taken much to make it seem like a more authentic setting instead of just a randomly chosen state name, a street, the name of an interstate, anything.