Was he a full-time student from January through May? If so, unless he provided over 50% of his own annual support, he is probably your dependent.
If he is NOT your dependent, they you may try allocating 100% of the 1095-A to his tax return for those 8 months (the 4 months will still need to be on your tax return).
If your income is fairly close to the 400% poverty level, then try contributing to a Traditional IRA to lower your income down to 400%. The would greatly lower the repayment.
