Does whatever you own become community property when you get married?

No, your property remains your separate property during your marriage unless you do something to change that status.   During marriage, you and your spouse can change separate property to community, or community to separate–if you do it in writing.  If it is real estate, have your signatures notarized.

The California default rule is that all property acquired during marriage from work or earnings is community property.  Husband and wife can change that rule — in writing — before or during marriage.

Separate property is what is owned before marriage or acquired by gift or inheritance.

If your separate property is money, you could change it to community  by putting it into a joint bank account.  If you use a large lump sum of separate money for a down payment on a house, keep good records.  You can get that money back, without interest, when you sell the house.

If your separate property is an inheritance, keeping in in a separate account will assure it remains separate.

Do you know what you did by getting married?   By law, that “I do” included a promise to deal with your spouse with “highest good faith and fair dealing.”  The relationship you are now in is a “confidential relationship” which imposes that obligation.  “Neither shall take any unfair advantage of the other.”  Story on National Public Radio said 87% of people lie to their spouses about money.  Breach of fiduciary obligation.

Squandering money on gambling, affairs, lavish gifts to your mother  he did not agree to–you owe it all back to the community.  One husband owned up to spending $50,000 on his mistress over five years; he will pay now ex-wife $25,000 from his share of the equity in the house.

As part of that fiduciary obligation, you are entitled to access any books he keeps for any transaction– inspect and copy.  On request, you will give your spouse true and full information of all things affecting any transaction which concerns the community property.

If he did not consent to a transaction that concerns community property, you own him an accounting; you hold any benefit or profit as a trustee for him.