When you get married your new spouse owns half your assets.
It is a commonly held myth that the instant you get married all your assets are now equally shared. In California any asset owned when a person gets married is their separate property and stays their separate property unless transmuted (transferred in writing) to community property or commingled to a degree that is no longer traceable. However, any assets acquired during the marriage by the efforts of either party will generally be considered community property. At divorce the burden is on the spouse claiming a separate property interest in an asset to prove the property was owned prior to marriage. At trial the judge will confirm each party’s separate property to the owner of the separate property and divide the community property among each spouse.
Living with someone for a long time creates a common law marriage.
California abolished common law marriages in the late 1800s; therefore, simply living together and claiming your married will not create a legal marriage recognized by the State or Courts. California requires a marriage be solemnized and documented to be legally recognized. See California Family Code §300 which provides:
(a) Marriage is a personal relation arising out of a civil contract between two persons, to which the consent of the parties capable of making that contract is necessary. Consent alone does not constitute marriage. Consent must be followed by the issuance of a license and solemnization as authorized by this division, except as provided by Section 425 and Part 4 (commencing with Section 500).
(b) For purposes of this part, the document issued by the county clerk is a marriage license until it is registered with the county recorder, at which time the license becomes a marriage certificate.