But Emma can tell when people lie and Emma knows Regina doesn't love Henry.
What episode was this determined in? I don't recall it.
In the first or second episode, when Emma was still planning to leave Storybrooke, she directly asked Regina if she loved Henry. There was no character to speak to, but she immediately canceled her plans and took a room at Granny's (where she first saw Gold, who was collecting from Granny.) She clearly found it necessary to stay precisely because Regina did not love Henry. Emma's need to save Henry was her motivation for pretty much the entire season.
Speaking of motivation, wasn't the origin of Henry's book just dropped? Or did I miss a throwaway line or quick scene while in the kitchen for refills or whatever?