(a) Eligibility. To be eligible for naturalization under section 319(a) of the Act, the spouse of a United States citizen must establish that he or she:

(1) Has been lawfully admitted for permanent residence to the United States;

(2) Has resided continuously within the United States, as defined under § 316.5 of this chapter, for a period of at least three years after having been lawfully admitted for permanent residence;

(3) Has been living in marital union with the citizen spouse for the three years preceding the date of examination on the application, and the spouse has been a United States citizen for the duration of that three year period;

(4) Has been physically present in the United States for periods totaling at least 18 months;

(5) Has resided, as defined in § 316.5 of this chapter, for at least 3 months immediately preceding the filing of the application, or immediately preceding the examination on the application if the application was filed early pursuant to section 334(a) of the Act and the three month period falls within the required period of residence under section 316(a) or 319(a) of the Act, in the State or Service district having jurisdiction over the alien's actual place of residence;

(6) Has resided continuously within the United States from the date of application for naturalization until the time of admission to citizenship;

(7) For all relevant periods under this paragraph, has been and continues to be a person of good moral character, attached to the principles of the Constitution of the United States, and favorably disposed toward the good order and happiness of the United States; and

(8) Has complied with all other requirements for naturalization as provided in part 316 of this chapter, except for those contained in § 316.2 (a)(3) through (a)(5) of this chapter.

(b) Marital union—(1) General. An applicant lives in marital union with a citizen spouse if the applicant actually resides with his or her current spouse. The burden is on the applicant to establish, in each individual case, that a particular marital union satisfies the requirements of this part.

(2) Loss of Marital Union—(i) Divorce, death or expatriation. A person is ineligible for naturalization as the spouse of a United States citizen under section 319(a) of the Act if, before or after the filing of the application, the marital union ceases to exist due to death or divorce, or the citizen spouse has expatriated. Eligibility is not restored to an applicant whose relationship to the citizen spouse terminates before the applicant's admission to citizenship, even though the applicant subsequently marries another United States citizen.

(ii) Separation—(A) Legal separation. Any legal separation will break the continuity of the marital union required for purposes of this part.

(B) Informal separation. Any informal separation that suggests the possibility of marital disunity will be evaluated on a case-by-case basis to determine whether it is sufficient enough to signify the dissolution of the marital union.

(C) Involuntary separation. In the event that the applicant and spouse live apart because of circumstances beyond their control, such as military service in the Armed Forces of the United States or essential business or occupational demands, rather than because of voluntary legal or informal separation, the resulting separation, even if prolonged, will not preclude naturalization under this part.

(c) Physical presence in the United States. In the event that the alien spouse has never been in the United States, eligibility under this section is not established even though the alien spouse resided abroad in marital union with the citizen spouse during the three year period.