I am in the same boat actually, except I sucked on just the tip of his penis for a few seconds and he precame a little bit. I put a condom on him and finished him off. The next day, I felt somewhat sick and then the next I'm feeling a little more sick (sore throat, headache, tummy ache). Now i'm worried about HIV, gonorrhea, and chlamydia....
Chances of an STD from giving a man oral sex for just a few seconds are really low.
HIV is not a concern, and chlamydia is a risk in theory, but most experts have never seen a case of oral chlamydia, so it's not much to be concerned about.
Gonorrhea is a higher risk, but again, after just a few seconds, and at least in the case of rocketpower111, where there was no deep throating, it's probably nothing to worry about.