Last year when we filed our taxes the guy where we did it told us to file married because we were living together but we are not legally married. This year we are going to do our taxes but are doing it separate because she doesn't live with me is it OK to do this?

Yes - if she doesn't live with you and you are not legally married then you are definitely single.

Further, you need to determine if you filed correctly LAST year. You may be considered married under a "Common Law Marriage" statute that is available in eleven states plus the District of Columbia.

You can Google Common Law Marriage to find which states still recognze common law marriage.