Achilles knew there were uncertainties between Polyxena and Patroclus, but this wasn't about either of their differences. There was a task ahead and it was all Achilles cared about.
He rested a hand on Patroclus' shoulder when he appeared with a nod, a quick embrace and then slowly pushing him towards the door.
"This is no time to think about that," he instructed his friend. "You're going to have to block your mind for Briseis' sake right now." It was a command or Patroclus would break and Achilles couldn't see that.