"Would you not?"
Amy stayed silent at Henry's question. It was a 'what if' question that she has no answer to. She doesn't have to ponder about it when it did not and will never happen in the first place.
But Henry wanted to hear what is her answer about it. It is his fear of losing her that is making him overthink a nonexistent scenario that is driving him mad.
"Why won't you answer me, Amy?"
"Henry, I think it doesn't matter what my answer is. It didn't happen and it won't ever."
"But if it did, will you marry Ash?"
"You are jealous over nothing and you know that," Amy's patience is running thin with Henry's illusions but she can't blame him. She knows where his fear is coming from. It was due to his experiences in life ever since he lost his family, but it's annoying that it makes him doubt her.
"I just want to hear your answer," Henry insisted.