He has to decide whether or not he ought to allow that to mollify him, and he stares sulkily at the floor for a moment or two, processing Watson's reactions to Holmes's suspicions. He doesn't doubt, still, that Watson is interested in Mary, or at least would be, and a part of him struggles with this idea. He's selfish, he doesn't want to give Watson up, but maybe some of this fear stems from the fact that on some level he feels he ought to.

"If you would prefer that, then why not take it?" he says, with some of the venom in his voice turning to hurt.