@Larien,
Personally, I would stop sending personal messages to this person, since it's known he publishes them.
Are you talking about yourself and messages you've privately sent, or others? If it's you, stop sending messages. If it's others, you've got to examine whether that person is able to speak for themselves. If they are, let them figure it out.
Larien, you have to differentiate between bullying and getting into the middle of 2 people who are both perfectly capable of taking care of themselves.
If it's you, learn to take care of yourself by stopping the behavior that is causing this person to accost you.
It's a website for God's sake. It's not as if this person is showing up at your front door. You can in a virtual way walk away from this person.