It sounds like you are still using the same account that was used for previous tax returns that you used when you were married and filing a joint return. It is very hard and messy to remove the "spouse stuff" from an account, so if you are no longer married you should start a new account with a different user ID for your Single filing status. That way there will not be any mention of your ex spouse, and you will not encounter errors related to him as you enter data or try to file.
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-online/00/25596