You should always use a unique password for every website account you have. Don’t log into Facebook with the same password you use for your bank, for example. If one website account gets compromised, as happens quite often these days, a hacker that gains your username/password can go try that combination on any other website.
The more frequently you use the same password in multiple places, the greater the chances that multiple accounts get compromised. To aid in the daunting task of using a unique password for every website, employ the use of a password manager, of which there are many ranging from free to yearly subscriptions.