Oral sex is not considered a risk for HIV. In the 40 years that HIV has been studied, they have repeatedly found that in relationships where one partner is positive and one is negative, and they only engaged in oral sex, no one ever caught HIV that way. This is due to the fact that human saliva considered a hostile environment in which the virus cannot survive, much less replicate. Therefore, if all you ever do is oral sex then it's highly unlikely that you'll ever catch HIV.