I receive disability benefits from Social Security, and every year they do a phone interview. In the past, I was asked if I was married, and I said, no. They also asked if I lived with anyone I considered a spouse. If I was with a partner, I cannot answer single or married because none of them are true.
According to the Social Security Handbook:
306.1 What is the definition of spouse for Social Security purposes?
You are considered a spouse for Social Security purposes if you meet the conditions in either (A) or (B) below at the time you apply for benefits:
(A) Under applicable law:
You and the worker were validly married; or
You would have the status of a husband or a wife with respect to the taking of intestate personal property;
(B) You entered into a ceremonial marriage with the worker that was invalid under applicable law because of an impediment resulting from a prior marriage or its dissolution; or a defect in the procedure followed in connection with the alleged marriage, provided:
You married the worker in good faith, not knowing of any defect at the time of the marriage;
You were living with the worker in the same household when he or she applied for benefits (unless you were divorced from the worker at the time); and
For benefits payable prior to January 1991, there is no other person who is or was entitled to monthly insurance benefits on the worker's earnings record as his or her spouse and who still has status as the worker's spouse.
So, it's going to depend on the laws of your state. If you died without a will, would your partner be legally entitled to your personal property?