A question I received:
I have Facebook, do I need to treat WhatsApp like my Facebook massages, what's the difference? And what's with my previous messages?
Any messages being sent and received are technically E2E encrypted, the "problem" lies where either party backups their data. In short any message sent to anyone who backups their data (to the cloud) isn't E2E anymore.
E2E is a high level of encryption. Not having it doesn't mean your data isn't secure, but say, the court ordered google to give the FBI access to their servers then your data can be passed along.
So now back to WhatsApp and Facebook. No, your previous WhatsApp messages won't be seen by facebook, and yes you should've never sent anything you didn't want the government (or technically the admin of whichever cloud backup used be it google or iCloud) to see. Unless your absolutely certain neither party backed up their data.