The only things that can decrypt a FileVault volume are
- the passwords to your user accounts that you gave access during FileVault setup, and
- the recovery key (24 characters) that you received (and should have written down) during FileVault setup.
If you no longer have the recovery key, and you're concerned about forgetting/losing your account password, you can go to
System Preferences > Security & Privacy > FileVault and click
Enable Users... to allow more user accounts to decrypt the volume.
Alternatively, if you don't want other accounts to have that ability, you can disable and then re-enable FileVault to get a new recovery key (but that may take a long time).