married filing separately during divorce in California

I am in the middle of a nasty divorce and my ex won't provide me with tax documents unless I agree to file jointly. I don't want to file jointly because they have underwitheld and want me to pay their tax bill. How do I fill out form 8958 when I filed for divorce January 31 so have 1 month on "community" income and 11 months of "separate" income. I have a couple of their paystubs so can guess at their income during that month but they refuse to share a W2 and other paystubs. We also have a jointly owned rental property and they won't provide me with receipts for repairs though I have most of the other information. How do you file taxes when someone withholds information from you?

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