Regarding Nicky's interest in the neighbor (which is not quite the same as my interest in the neighbor):
Nicky doesn't like people food
Nicky doesn't seem interested in food smells
Nicky does not like shrimp
I don't think the neighbor is dead, because both he and his girlfriend would have to be dead; and if so, who keeps driving their two cars?
My guess is that they may have gotten a cat.