Now you get to watch her leave out the window
Guess that's why they call it window pain
Em stresses on the word window here to indicate her leaving in a stealthy manner; people normally exit via doors, but in this case, he’s alluding to the idea that Kim snuck out on him. The window pane/pain play on words is to indicate how much he misses her. You wait longingly for someone by leaning on the window pane. Her absence hurts him.
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