Can I file as single even though my divorce is not final? I did not live with my spouse at all this year.

Whether you are considered married or unmarried will depend upon state and federal law. Tax law says an individual legally separated from his or her spouse under a decree of divorce or a decree of separate maintenance shall not be considered as married.

Many couples are legally separated but are still considered married under state and federal law. If your divorce is not final, you are still married unless your state allows for a decree of separate maintenance. Your attorney should be able to determine whether your current legal status meets the definition of a decree of separate maintenance. 

For your federal return, you can file as Head of Household if all the following apply: you and your spouse lived apart all of the last 6 months of the year; you file a separate return from your spouse; you paid more than half of the cost of keeping up your home for the required period of time; your home is the main home for your child, stepchild or foster child for more than half the year (a grandchild does not meet this test); you claim the child as a dependent.