I work at a US embassy overseas. Am I a resident or non-resident of Massachusetts?

My spouse is working in a US embassy overseas and gets paid by the federal government. We will be living here for 5 years. Before leaving we lived in Massachusetts, and are registered to vote and our licenses from Massachusetts. We do not own any property and only visit for about 2 weeks a year. We are not sure if we will go back to MA when we return. For state tax purposes are we considered residents or non-residents of Massachusetts? Their is no state income tax shown to be taken out on our w2. Thank you I appreciate the help!