The form doesn't ask for marital status, only has space for individual and spouse. You just don't fill in the 'spouse' portion. Under "type of debtor' you'd just check 'Individual'.
As for your STBX spouse, if there is ANYTHING that you think he might come back to you for money for, then you really should add him to your creditor matrix. This will prevent him from trying to collect money from you later for just about anything. If there's nothing like that, then leave him out of it and he should never know. I would do one thing though - if your STBX reads the newspaper, you might want to check to see if your local newspaper still publishes the names of people who have filed for BK - some papers still publish that info, which sucks but who knows.