YOU CAN PRY THIS HEADCANON OUTTA MY COLD DEAD HANDS -
So okay. They were friends. They HAD to be friends. Why would Jelly (Herbert) let Snatcher into his house ON THE SECOND FLOOR that night? How did Snatcher find out Boxtrolls weren't malicious when previously it was only Jelly who dared to get to know them? Is it coincidence and mere symbolism that Jelly's favorite snack is completely non-dairy and would be safe for someone hanging out with him to eat if they had a condition that required that? Huh? HUH?

And then I took it one step further and was like "Villain befriended hero...villain crushed on hero...hero didn't like villain in that way but still liked him platonically...villain got salty and blamed hero's actual love interest for ruining the relationship...villain goes megalomanical...hero is done with villain now but is sad about their friendship."
That may sound incredibly specific but this trope has happened to me multiple times. (If you've seen Monsters University, you know.)

I have a whole fanfic about this. It is purely angst, though. If you want the proof: https://archiveofourown.org/works/123...
However, this is also canon to my main 'verse in which...uh...RWBY crossover. He moved on. ;-)