Arnold Schwarzenegger -- 200 Million Reasons To Stay Married to Maria

Arnold Schwarzenegger has 2 very good reasons NOT to finalize his divorce ... and one has to do with writing a big fat check to Maria Shriver.

As you know ... Maria filed for divorce in July, 2011, after finding out her hubby had been banging the maid and produced a son.

Sources familiar with Arnold's situation tell TMZ ... there's no prenup so under California law it's pretty simple -- 50/50. And our sources say there's no real issue over custody of their only minor child.

So why, you ask, has this divorce dragged on 2 1/2 years? We're told Arnold doesn't want to write a gargantuan check to Maria ... and we know how much -- and it hurts.

Sources tell us their net worth is around $400 million. We're told Arnold knows Maria is entitled to half -- but knowing it and watching around $200 million leave your bank account are 2 very different things.

As for the second reason Arnold's in no hurry ... we're told he's getting pretty serious with his girlfriend, physical therapist Heather Milligan. If Arnold gets divorced, the pressure's on for him to pop the question ... and Arnold's not necessarily a one woman kind of guy.

Just ask the maid.