If you wish to unlink your Facebook account from your misterb&b account, you will have to go into your Facebook settings and click "Apps and Websites". Here you will be able to remove the misterb&b app, and both accounts will be unlinked.
Then, if you wish to log into misterb&b, you can use the same email address as your Facebook account, and then click on "Password forgotten". You will then be sent an email, giving you the option to add a new password for your misterb&b account. Please note that this will not affect your original Facebook account details.