There is no legitimate chance that you would acquire HSV 2 from a roommate unless they are your sex partner. I would recommend that you use your own towel, but other than that, no precautions are needed. Period. I also wonder if your roommate’s diagnosis is correct, given the high rate of false positive in some populations for this test. If he was diagnosed only by blood test, it would be worth looking at the numbers associated with that diagnosis and if low, confirmation should be done.
Given the rate of false positives, you should carefully consider the IgG test. It is true that 80% of those infected don’t know they are infected, so you could the IgG and confirm a low positive if it happened with the western blot OR begin with the western blot though it is more expensive.