Understand that how you file your taxes has nothing to do with one's debt liability. If your spouse is not a cosigner on the loan, then they have no obligation to pay one single penny of the debt.
However, if you are not current on your loan repayment terms, any refund can be (and probably will be) garnished to pay towards that debt. In the case of a joint return, if the one that does not have a legal obligation to pay it includes form 8379 with the joint return, then their portion of the refund will not be garnished. Understand that their portion of the refund is determined by there share of the tax liability (which is rarely 50%) and their share of taxes withheld from their paycheck (which again, is rarely 50% of any refund due.)
