Amy was overwhelmed by Henry's confession even if she can already feel what he just confessed. Somehow deep inside she knows that Henry's actions towards her are real and from the heart and not just contract-driven. But him saying that she's the reason for him being alive is on a different level.
She knew that Henry had a dark past but not to the point of killing himself. She just wishes that she can say those three magical words back to him in full confidence, but not yet, her heart is just not ready.
Henry felt like an enormous rock has been lifted from his chest. He had never felt so featherweight before and it was just so heartening that he knows he did the right thing. Amy still being in front of him and didn't run away means that she accepted his feeling even if she have not voiced out her feelings for him yet.
