The wait of the realization is heavy, because it occurs to him now that he's started to believe. He believes her words, he believes what the Autobots have been trying to accomplish. He doesn't know how, but he's just come to understand its truth deep in his spark, like something instinctive. He can't see any falsehood in her - in any of them.

And that leaves something even more painful to contend with.

He vents harshly, traces of exhaust escaping his pipes. His engine rolls uncomfortably, and he can't really think of what to say. He just feels so intensely miserable for a moment that it's overwhelming, and his frame shakes with idle rumbling.