Just because the ejaculation occurs outside the body of the partner, it does not mean that there is no risk. Penetrative sex without a condom is risky because the pre-ejaculatory fluid that is excreted as a lubricant when the person is sexually excited can have the virus if the person is HIV infected. Oral sex, though less risky than vaginal or anal penetrative sex, still caries some risk, especially in the event of his discharging in the mouth. To some extent but not entirely this also depends upon the health of the gums. I can only conclude that you are definitely at risk and should get yourself tested immediately and again after six months from the exposure.