Domicile is a legal term. Your domicile is your permanent home, the place you intend to return to after being away. You can have only one domicile at a time, but you can have more than one residence.
You have to pay Massachusetts tax if you are a Massachusetts resident, even if your domicile is elsewhere. Each state has its own definition of a resident for income tax purposes. Here is the Massachusetts definition of a resident, from the Form 1 instructions.
"You are a full-year resident if your residence (domicile) is in Massachusetts or if you maintain a permanent place of abode in Massachusetts and during the year spend more than 183 days, in the aggregate, in the state."
Read the definition very carefully. Note that spending any particular amount of time outside of Massachusetts does not necessarily mean that you are not a resident.
Of course, you also have to pay Massachusetts tax on any income that you earn in Massachusetts, even if you are not a resident.
Finally, I am not a lawyer and I cannot give you legal advice. If your domicile or residence is not clear, you might wish to consult a tax lawyer in Massachusetts who can review all the details of your situation and advise you as to your domicile and residence, and whether you have to pay Massachusetts income tax.
