the HTML Editor should not be in a repeat region.
next to each comment, you would have a link to another page to replay to it. This link will send the comment ID as a querystring variable.
on the next page, have the HTML Editor text box to enter the reply, and a hidden form element that is set to capture comment ID form the querysting.
in the insert record behavior, set the reply_id column to use the hidden form element. and the comment column to use the HTML Editor instance.