He's frustrated. Frustrated with you--irritated with himself for letting you get hurt in the process. Optimus couldn't bear to see you all broken up and beaten. Why didn't you listen?

"I told you to fall back." He scolds, optics scanning you for any more injuries. He sighs. Optimus's not sure if he enjoys your stubborness that much.

He's worried for you, but he tries not to show it. He doesn't want you getting hurt time and time again because of him. You're his sparkmate--his everything.