Boys cry too, and that's fine.

Whether you are mom, dad, brother, sister, uncle or aunt - remember that all your conflicts affect children. So be so kind as to shove your aggression and nerves up your ass and/or at least try to protect him from this child, or explain the situation humanly to him, and not throw yourself into the abyss of your own problems. You wanted an emotional slave with an unstable psyche? Well done. Got.
To the victims of this behavior, I can only express moral support. It will be hard, but you can handle it.

Doesn't it remind anyone?