Galahad considers this seriously; Susan deserves a thoughtful answer. Despite his feelings for Lancelot -- like a long-lost cousin, whose wellbeing is somewhat Galahad's responsibility -- when he examines whether it matters to him that Susan and Lancelot marry, or don't marry, he finds nothing. Susan is his friend and fellow scientist. Her comfort and certainty are what matter. Love is not always enough for marriage.

"I'm not uncomfortable," he tells her, and he means it.