Why do I feel so sad when my boyfriend leaves?

Or when I leave his place. I feel so empty and numb and just sad. I do not understand why. I'm pretty sure he does not experience this. We have been dating for 8 months.
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Thank you for all the answers! Relieving to hear it is normal - it’s my first relationship ever (I have very strict parents lol so I couldn’t really date until I was 17) so i didn’t know
Why do I feel so sad when my boyfriend leaves?
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