October 21, 2011 | Legal Permanent Residents (LPR), Naturalization
A. The issue of taxes and naturalization pertains to the naturalization requirement that an applicant demonstrate that he or she is a person of good moral character for the statutory period. Because you have been a permanent resident for over five years, you can apply on your own. As long as you have paid taxes for the past five years, your having filed taxes as single since your separation should not be a problem.
If you were applying under the three year rule (green card holder for three years and married to a U.S. citizen for three years) then your tax filing status WOULD be an issue for USCIS. However, once you apply on your own under the five year rule (green card holder for five years), all that matters is that you have properly filed taxes in each of those five years.