"Well, I am apologizing because Icarus and Meryl already knew," Lucyna said. "I only didn't trust you, but that changed now. You let one of us get the Manipulator power."
While he didn't get it in spades, Billy also got that power. He could even turn that into a skill if he wanted under the right circumstances, but that would let the others know. He will only absorb the mana and effect of those relics once he gets better at it and at the right time. Billy got exhausted when he absorbed the effects of that ring, and that was a weak relic, after all.
Putting that aside, Billy decided to ignore what Lucyna said. Being all nice and understanding would make them become friends, and his plans wouldn't change regarding his Posture with those three. No matter what happens, Billy couldn't see himself killing his friends, the people he really was close to. However, he needed to be prepared to kill those three if it was necessary, and he won't have time to hesitate.