Mac doesn't remember my password
Since you are referencing having to use a recovery key to log in, it sounds like your Mac has FileVault 2 encryption turned on. Are you expecting to turn on your Mac and have it automatically log in as you? 

If that's the case, the encryption does not have that as an option. You must provide your account password or the recovery key in order to unlock the encryption before the OS can boot.

If my understanding is incorrect, would you please provide more details about the problem you're seeing?