"Nina has to stop talking to me or something bad is going to happen. I'm sorry, tough."
It sounds like this is a threat directed at Nina. It's important to remember that threats are never okay and can have serious consequences.
If you are concerned about this situation, it is best to seek help from a trusted adult or authority figure. You can also report the threat to the appropriate authorities.
Remember, it's never right to threaten or intimidate someone.