Because you are married, you cannot be treated as single. You can file a joint return, or you can opt to file as “married filing separately.” However, if spouses live apart and meet certain tests, one may qualify to file as head of household instead of married filing separately. To do this, you must have a qualifying person live with you (or a dependent parent even if not living with you); a spouse is not a qualifying person.
An employer reimbursement or allowance arrangement that requires you to adequately substantiate business expenses to your employer, and to return any excess reimbursement.