This is one of the most tragic points in the novel, in my opinion. Let us not forget the context of this trip to revisit Madame. They believe that Madame and their former headmistress is able to grant clones who are sincerely in love a deferment so that they can enjoy a stay of execution before they are called to donate their organs. For Tommy and Kathy, this is the only hope they have before Tommy is called upon to continue the process of harvesting. It is therefore incredibly tragic when they find Madame and their former headmistress, only to be told that what they have heard is an absolute myth and there is actually no such deferment possible, even for those who are sincerely in love.
This represents the last extinguishing of the spark of hope that Tommy and Kathy had for any kind of future. After this, all they have to look forward to is their own completion and separation. Tommy and Kathy are shown to face a grim and unyielding future which has no sign of relief or let up.