"The Nut-Brown Maid", also known as "The Nut-Brown Maiden", is a ballad included by Thomas Percy in his Reliques of Ancient English Poetry.
The Nut-Brown Maid Wikipedia
A man and woman talk of women's fidelity, he disbelieving, and she producing the nut-brown maid as proof. They discuss her story. Her love comes to her, a knight but banished. She tells him that she loves him alone. He tells her that he must go to the greenwood, and she says that it grieves her. He asks if she would not find time easing her and urges her to let it, and she declares that she would go with him to the woods. He warns her that men will slander her for it, that she will have to take a bow as if a man, that if he is caught and executed, no one will help her, that the way will be hard, in the wild and exposed to weather, that meals will be scarce and beds non-existent, that she will have to disguise herself as a man, that he believes she will give it up quickly, that being a baron's daughter and he a lowly squire, she will come to curse him for this, and that he might fall in love with another woman, but to each one, she retorts that she will still come, because she loves him alone.
He tells her that he is not, after all, banished, and she says she is glad but knows that men are fickle. The man assures her that he will marry her, and that he is, in fact, an Earl's son.
Matthew Prior's 1709 poem Henry and Emma is based on "The Nut-Brown Maid".