Dennis Quaid and Wife Back Together -- But They Can't Stop Divorce

Dennis and Kimberly Quaid are one happy family again ... with one big problem -- they can't stop their divorce from going through.

TMZ has learned ... before getting back together, both Dennis and Kimberly signed the divorce documents and they are sitting on the judge's desk right now, but we're told the paperwork is going through the system and the judgment will become final.

As we first reported ... a source close to the couple told TMZ back in October, "Kimberly is fed up with Dennis' cheating and wants out of the marriage. He's not a good husband." She was gunning for primary physical custody of the twins, as well as spousal support.

It's not the couple's first change of heart. Back in March, 2012, Kimberly filed for divorce but withdrew the petition two months later.