Then I think it comes down to whether or not you feel you need to protect yourself (financially) from him.
I separated from my husband for over a year before I filed for divorce. It was very stressful worrying about things like him getting a DUI and my insurance going up as a result. Or him not paying his taxes and the IRS coming after me. Or any other bill collectors for that matter.
I could have stayed married living separately forever if it wasn't for those fears. (Okay, maybe not forever, but protecting my assets was the main reason I decided to divorce.)
L