I'd be surprised, and I'd assume it was either before us as a couple - why? Because she has strongly held views on cheating, and would not do so...and is scared of needles, so not likely to be injecting substances!
I'd be a supportive, loving wife. Sure, a few things may have to change - to protect me and our daughter, but given the nature of our relationship - we are at the lower end of risk for transmission (not likely, but not FREE of transmission either) - I'd get tested, and we'd go from there.
I took my vows seriously, and a life-threatening illness would not change that - in sickness and in health, remember?
(That being said - this is how I THINK I'd react...given what I know about my wife....should the situation be different - cheating etc...I'd like to think I'd still do the same!)