Legal Question in Family Law in Massachusetts

Legally, you are not responsible for your girlfriend's bills or expenses. Your girlfriend is responsible for her own expenses, bills, and debts, regardless of what the mother says. I don't have enough facts to know whether this is a good idea, but your girlfriend should know that she can revoke a power of attorney at any time - it would be a good idea to have an attorney assist in this regard.

Your 22 year old girlfriend is an adult. As such, only she can grant "power of attorney" to another person to act on her behalf. Such power is revocable by the grantor at anytime and for any reason. That is, the "attorney-in-fact" (person with the power) can only act on the grantors behalf as long as he or she has permission from the grantor. Another way a person can obtain authority over the financial affairs of another is to seek guardianship from the Probate and Family Court. This requires filing a petition for guardianship. The petitioning party must then prove that the subject person is incompetent to handle their own affairs and would benefit from the appointment of a guardian. This usually requires medical evidence.

In your situation, it sounds like your girlfriend's mother has been paying her bills. If your girlfriend granted power of attorney to her for this purpose, your girlfriend is still obligated to pay her bills. You are not liable for them unless they are joint debts (e.g. you co-signed a loan or are a co-account holder on a credit card). Since you are not married, your girlfriend is responsible for her own bills regardless of who she lives with.