Way back on season one, in episode 13, “What Happened to Frederick,” Prince Charming went on a quest to get some water from Lake Nostos. Lake Nostos was guarded by a siren. The siren herself, could trap and kill anyone who ventured into the lake by transforming herself into anyone.
When Charming confronted her, she changed into Snow and tempted Charming but he resisted.
He said:
“No. I don’t want an illusion. I want a reality or nothing.”
This line reminded me of Regina’s gift to Emma in the winter finale. Emma and Henry will have always been together, their future will be real but their past, their memories won’t be.
In a sense, it’s similar to what Charming realized when he faced the siren. An illusion, however powerful it is, it isn’t a real, a true happy ending.
And I think that’s why Hook came back for her because he realized, Emma’s happy with Henry but their life, it isn’t real. Their memories are an illusion. It’s fake. And because he loves Emma so much and knows what she is, the epitome of true love, he realized that she deserves better than that.