From the promo for episode 21, it looks like Henry may play a pivotal role in helping his mother to believe by taking matters into his own hands. He says he trusts her and then falls to the floor. There has been some speculation that he eats a poisoned apple meant for Emma, fully believing that she has the power to save him with a mother's true-love-for-her-son kiss. She did manage to set Graham free from the curse so he remembered, so it's entirely possible.
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy