I think it means if you hurt my friends, I will kill you.
The guy that was always wearing black and wanted to dump the fish into the lake
Answer: "You have to keep lying, and soon no one can trust you."
Explanation:
If we lie about something, we must usually invent the whole story to make it convincing. For instance, if a boy lies to his parents that he did his homework, while, in fact, he was playing computer games, he must prepare the story in advance. He must prepare answers to their further questions - which subject it was, what the homework was about, etc. This just creates more problems, because the boy will find himself in the whole web of lies. Moreover, if he gets caught by his parents, they will not trust him anymore. This is why it is much more simple to tell the truth and avoid further problems.
