Ending Meaning *Spoiler Alert*
If I can beg to differ with some other posters, I think the meaning of the ending is relatively straightforward. Mrs. Stone had fallen so far that she didn't care if her stalker was going to love her, or kill her.
She was indifferent at that point. So it (arguably) makes no difference to the viewer what he was (i.e. a lover or killer) because the point was really that she didn't care. That's a pretty heavy statement to end it on right there.
For what it's worth, there are a lot more lovers in this world than murderers, so I'd say the odds are in favor of him becoming a cheaper version of Paolo.
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what is the purpose of this really?