Soulmates

I got this from a writing prompt, so I hope y'all don't hate it. The prompt is: "When people are born they are assigned a soulmate. They have an original song in their head that only them and their soulmate know. A person just broke into your house and you're pretty sure they're here to murder you. They're humming your song under their breath." (I couldn't think of anything else for the title)