yes -- you can get FA, back taxes oweing or past due child support will not impact the awarding of federal or state FA.
however, as a non-traditional student you will have a few extra hurdles to jump. First -- nursing tends to be a fairly competitive program, so just getting admitted can be tough. Second -- you can recieve FA, but the financial aid is limited; you will still need to work (probably full-time) in order to pay living expenses.
I qualify for pell grants, colorado state grants and my university also awards me an institutional grant -- and I attend a 4-year university which is very cheap in comparison with most state universities. Even with all that financial aid, it only covers 12 hours of tuition, required fees and books. you will need to work in order to pay for your living expenses -- I work ~35 hours a week, so it is doable.
I am also a non-traditional, low-income college student. Your best bet is to attend a community college for two years and earn an AA degree. Not only is the CC cheaper but it is set up for non-traditional students, so there are multiple classes at different times to work around work schedules.
most community colleges offer a guaranteed transfer program to a local 4-year university -- and many offer transfer scholarships. Make sure you meet with a counselor and go over requirements, etc.
unless you actually get married, your fiancee's income will not be counted towards your financial aid determination.