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It is very rare that spousal support lasts indefinitely. Unfortunately (for marriages that last greater than 10 years), there is no hard and fast rule on how long the courts will require one spouse to continue paying alimony or spousal support (the two terms are interchangeable), but this article here gives you a good overview of the factors that the court will be looking at: http://www.divorcenet.com/states/california/cafaq07#b
To petition the court for a change in support orders, you can hire an attorney (probably the best way to leverage your position for the best possible outcome), or you can petition the court yourself "pro per" - the California Courts have forms and information to assist you (including a packet on adjusting spousal support) here: http://www.courts.ca.gov/1038.htm