Generally you should not be accessing your spouse’s Facebook account unless you would normally do so. For example if you had a shared Facebook account during your relationship, it would still be acceptable for you to access it after a separation, but if you both had your own Facebook accounts and you would typically not access your spouse’s account during the relationship, you should not access it after separation either.
Even if you know your spouse’s password and set up the account for them, you are still not entitled to access their Facebook or other social media accounts. A good rule of thumb is, if the only reason you are accessing a personal account which belongs to your spouse is to see what they are doing and/or who they are taking to, then that action is not appropriate.