Thank you for your Social Security question.
The area treads on law that has not been fully contemplated by the government, but based on earlier decisions, I would think you need to meet the 9 month minimum.
There could not have been a common law marriage because same sex unions were not recognized prior to recent law. A "common law" marriage requires three elements: Live together (cohabitate), Hold yourself out as married, and Be legal under state law. In this case, you did not meet the third requirement until the law was passed allowing same sex unions.
More than likely, you will need to apply and again, you will likely be rejected, but you can push your case as a test case if you have the resources.
So, even with heterosexual couples if the 9 mo. is not met and one dies no SS.