With the intention to discourage Christopher from ever pursuing Serena, Charlton told him about how Serena sailed between two rivers, made him believe that she was his, how ready he was to fight for her, but in the end, when everything was said and done, she chose to abandon him for Geoffrey. Of course, he omitted some facts which were too private and sensitive, but the gist was there.
With Christopher seemingly not knowing what to say, their conversation ended with that. Then, after that day, he did not mention her anymore. So, he thought that Christopher have already been convinced that Serena was the most selfish and vilest woman in existence.
Obviously, if that have indeed been the case, he won't be feeling the way he did that instance.
