I was going to say, "Ban him from the site," but that wasn't what you were talking about.
Seriously, your primary concern must be your daughter. If there is the slightest possibility that his behavior is having a negative effect on her or if she is in the slightest danger, he must go. Whatever it takes. Whatever you have to do.
When you create a child, until she is a self-sufficient adult, she is THE focus of your life. Answer your question with her in mind.