Best password manager for my use case?

So I'm kind of tired of having more than one password, as anyone would be. But at the same time, I'm way more paranoid about security than I am knowledgeable about computer security.

Passwords must be encrypted and not decryptable without my password (obviously, can't imagine a password manager without this).

It needs to run on at least both Windows and Linux. I would also appreciate if it runs on BSD and MacOS in case if I ever try them for personal devices. Also Android if that's possible, but that's low priority, I don't log into stuff on my phone often.

It needs to be as close to 100% open source as possible, strongly preferably at 100% and under a FOSS license like the GNU GPL or MIT licenses.
As I said, I'm paranoid, and this means if they have proprietary code, I can't trust it.

It would also be nice if it has sane defaults making it simple to use, but this isn't a requirement since I'm willing to take the time to learn what I'm doing if it means more security.

I'd also appreciate anything you all think I should know when it comes to security with password managers.

Touch here for the full post on Network Security Noblemen tumblr