Do I really have to keep playing fair towards my soon to be ex-spouse?

The answer is YES! During marriage, after separation and until final disposition of all assets, spouses owe one another fiduciary duty, which is one of the highest duties of good faith and fair dealing. So, even though you may have a lot of anger, resentment, even hatred towards your soon to be ex-spouse, you must continue to fully disclose debts, assets, business opportunities, incomes, etc. The duty of disclosure applies equally to both community as well as separate assets and debts.  You must also maintain community property assets and separate property assets if you are the spouse managing those as well in accordance with the fiduciary duty.  

Upon serving of a petition for dissolution of marriage on your spouse, certain automatic restraining orders become effective. You can find them on the back of the summons, which is received together with the petition. They generally forbid parties to sell, convey, encumber community property without prior written consent of the other spouse. So, if you were thinking of selling your spouse's car or donating his clothing to Goodwill, you may want to think twice. If a fiduciary duty is breached, the court may not only award sanctions (attorney fees and costs) but also award the entire asset or proceeds from a sale of an asset to the other spouse. If, however, the nondisclosure is of a separate property in which the community has no interest, the court may not award the value of that assets to the other spouse.  Instead, the court may sanction the non-disclosing spouse.  

Divorcing spouses must also be careful about making gifts to their parents or romantic partners without obtaining prior written consent of the current spouse. If you do not, you may create a right of reimbursement. So, that diamond ring you gifted your girlfriend (and paid for from community funds) may cost you at least twice, if not more since your current spouse may also get attorney fees and costs.  

It is best to play it cleanly until the last asset is divided to avoid sanctions and a loss of assets.