He almost falls over with the extra weight on him, but struggles to keep upright. Flopping over would cause issues for both of them.

"I don't...I-I guess. I just...I don't know. I don't know." He wasn't going to stop feeling guilty for it, but her reassurance that it wasn't entirely his fault helped some. He'd wait for her to remember before really accepting the fact that she's not blaming him for it, though. That memory has to be terrible; it could change a lot.