Welcome to the forum. Thanks for your confidence in our services. The update probably was assignment to me as moderator.
This sort of notiice is understaably alarming. However, based on your desciption of hte sexaul event, you were at little risk of HIV. As for whether he actually is infected, that may not be certain: rather than being infected himself, perhaps he in turn was in contact with someone he learned has HIV. What more do you know about him? Apart from this notice, do you have reason to suspect he's at high risk, e.g. sex with other men? Injection drug use? Past imprisonment? Also, I assume you have no other high risk factors (simply dating male partners doesn't count as high risk) -- i.e. other known contact with infected partners? Drug use? And you're not a sex worker, right?
Obviously, you should continue to try to contact him. Alternatively, if the notice came from a third party -- especially a public health department -- contact them. They probably have more information about his infection status, risk factors, etc. However, if none of this pans out, it remains reasonable tor you to be tested. The best approach is to see a physician experienced in HIV treatment and prevention in person, then follow his or her advice about specific tests and timing. If uncertain about your personal physican's expertise, your local or state health department clinic would be a good option. Otherwise, you can have an RNA test at any time; around 90% of newly infected persons would have a positive result by then, so a negative result would be reassuring, although not conclusive. Then an AgAb (antigen-antibody, "4th generation") blood test at 4 weeks would make it virtually conclusive -- with perhaps a finally conclusive AgAb test at 6 weeks.
Do your best to stay mellow in the meantime. Even with a known infected partner, HIV is rarely if ever transmitted except by unprotected vainal or anal sex. The highest risk component of your exposure was your performance of fellatio -- and even that is very low risk. (If the male partner is infected, the average risk to the oral partner is estimated around 1 chance in 10,000 -- which is equivalent to giving BJs to infected men once daily for 27 years before infection might be likely. And even this assume ejaculation in the mouth, so your risk is lower still.)
The other issue, of course, is risk for STIs other than HIV. That risk also is very low -- and here too, the main risk is for oral infection from performing oral sex. When you seek care for testing, it would be reasonable to have a throat swab to test for gonorrhea and chlamydia.
I hope these comments are reassuring and otherwise helpful. Let me know if anything isn't clear.