If your instagram account is synced to your facebook profile means you can share stories and posts directly from instagram to facebook.
But if you want to separate both accounts, you can unlink or unsync instagram and facebook with few easy steps
Open the Instagram app on your phone and tap your Profile icon in the lower-right corner.
Tap the Menu icon in the upper right side.
Now, go to the Settings.
Select the Accounts Center and tap Account & Profiles..
Select the account you want to remove from your instagram account and tap Remove from Accounts Center
when the confirmation message appears, tap Continue.
Tap Remove on the account name you want to remove
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