20 CFR 404.347: “Living in the same household” defined.

Living in the same household means that you and the insured customarily lived together as husband and wife in the same residence. You may be considered to be living in the same household although one of you is temporarily absent from the residence. An absence will be considered temporary if:

(a) It was due to service in the U.S. Armed Forces;

(b) It was 6 months or less and neither you nor the insured were outside of the United States during this time and the absence was due to business, employment, or confinement in a hospital, nursing home, other medical institution, or a penal institution;

(c) It was for an extended separation, regardless of the duration, due to the confinement of either you or the insured in a hospital, nursing home, or other medical institution, if the evidence indicates that you were separated solely for medical reasons and you otherwise would have resided together; or

(d) It was based on other circumstances, and it is shown that you and the insured reasonably could have expected to live together in the near future.