I'm surprised that you slept on a heart that's worldwide
This could mean 2 things:
Slimkid3 is surprised that this person would sleep with another when the others heart belongs to others around the world, and they’ve hurt many before and probably more after.
That the said woman slept on (ignored or failed to see) his heart, which clearly had profound love for her, a heart so big it’s world wide. Then he goes on to say how one day she’ll open her eyes and see what she missed, meanwhile he’ll just be another fish in the sea.
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