I think she means that if you love or like some one and that some one does not love you the same, than no matter how cold he is with her, she still loves him or likes him like a spell on her.
I feel like she is saying she is frozen in time as in a spell. and she closes her eyes and feels the coldness of the wind,and sees only darkness but can not leave behind what she feels inside. can not let go of the love she holds and thats why she can't leave.She doesn't want the night to end.
What it means is that it's getting dark out,like night is falling, and because it's night it's cold, and when it's cold and dark don't you go home and leave...!? Now the point of saying there is a spell, is that love is keeping her from going, even though she is cold and it's dark out side. That's what her poem is saying.
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