Can I apply for citizenship if I am married for 10 years but have filling as single on my tax return because my husband had student loan?

It is impermissible and unlawful to intentionally state false information in a tax return. If a tax professional advises you that some peculiarity in the tax law permitted you to file as single, then your tax filings may not stand in the way of naturalization eligibility. If a tax professional advises you that you were not permitted to file as single, then you may need to file amended tax returns (and pay any additional amounts that may be due) and be prepared to explain, if applicable, how you misunderstood the legal requirement regarding your tax returns, in order to show that you do not "lack good moral character" and to be eligible for naturalization. There really is no substitute, however, for you to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibility and about strategy for naturalization, and who then could offer legal representation in the often complex application process.