The cause of action for annulment in New York State is generally fraud (DRL §140 (e)) and you'll need a lawyer. Check with a lawyer in your locale to discuss more of the details. The time limit is three years. The statute says this runs from the date the fraud was discovered, or could reasonably have been discovered.
Good luck to you.
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I must interject- if your partnership were created in New York City, and there are no property or children issues, this is a straightforward administrative process, and does not require annulment or other litigation.
I suggest you review this web page for 'termination procedures'- http://www.cityclerk.nyc.gov/html/marriage/domestic_partnership_reg.shtml#termination
Best of luck to you. If you require further assistance, kindly call.