) If he was infected, the chance you got HIV from any single episode of unprotected vaginal intercourse is something like 1 in 1000. So the odds you had HIV
at the time you finally went in for HIV
test were around 1 in 10,000. (Even without testing, many people would live comfortably with those odds and not worry about it.)
So what does the negative test result do to your chance of having HIV? Those odds are 1 in 100,000 times 1 in 10,000 (i.e., 0.000001 x 0.0001) = 0.0.0000000001.