Lancelot is successful at the tournament. He wears a favor made for him by Elaine—although he never usually wears favors (pitying her, he agrees to wear it, thinking it will aid his disguise). However, after he has knocked thirty or forty, Lancelot is set upon by three knights who penetrate his armor with a spear. He is carried, unconscious and wounded, back to the Castle Corbin to be cared for by Elaine.
Again, just as after he was found as a mad-man, Lancelot is cared for by Elaine. This posture is symbolic for their relationship: he can only stay with her while he is infirm and he will leave her as soon as he is better.
Before the tournament, Lancelot had been unable to tell Elaine he would not be staying for good; and now, as she nurses him, he does not have the strength too. At Corbin, Elaine and Lancelot are holding hands. Elaine keeps saying how she has him for good now. Finally, gently, Lancelot tells her they must speak.
When Lancelot tells Elaine that they must speak, he means to tell her that he is going to break his promise and will not be staying with her for good. This is the final heartbreak for Elaine, who believes that she finally has her Lancelot.