You can get all texts that follow a BR after a DividerText like this (in a sample console app):

  HtmlDocument doc = new HtmlDocument();
  doc.Load(MyTestHtm);

  foreach (HtmlNode node in doc.DocumentNode.SelectNodes("//text()[contains(., 'DividerText:')]/following-sibling::br/following-sibling::text()"))
  {
      Console.WriteLine(node.InnerText.Trim());
  }

Will dump this out:

TextToSelect1
TextToSelect2
TextToSelect3
TextToSelect4

The XPATH expression first gets recursively a text() node that contains a specific 'DividerText:' token, then get all following siblings BR elements, than gets all following sibling text elements.