Chris Rock -- I Was Just Tired of Being Married

Chris Rock filed for divorce from his wife of 19 years for one simple reason ... he wasn't happy in the marriage, sources directly connected to the couple tell TMZ.

One source says this will be a "simple divorce" and that there is no third party involved -- Chris just did not want to continue in a marriage that was not fulfilling.

Although our sources say the divorce won't be contentious ... obviously there is some bad blood. As TMZ previously reported ... Rock complained Malaak has been preventing him from seeing their 2 daughters -- and he is asking for shared legal and physical custody.

Malaak issued a statement making it seem like they jointly came to the decision to split -- but Chris' people fired back ... making it clear HE was the one who filed for divorce.