welcome to the Forum.  I will be pleased to provide some information.  Much of what I am about to say will confirm the research you have already done.  In doing so, I want agree that the risk of getting an STI from receipt of oral sex is lower than for most other sorts of sexual exposure however, I also want to challenge what appears to be your assumption the your insertion of your penis into your partners rectum need not be considered as part of your risk-it does.  Any sort of sexual exposure has some risk for acquisition of STIs, including HIV, and your insertional rectal sex was also risky, even as brief as it was (on the other hand, duration of exposure is also important and your receptive oral sex was far longer than your rectal sex so the risks do balance out).  Because of your (brief) rectal exposure, your concern should not only be for gonorrhea but also for chlamydia which is much more likely to be present and asymptomatic than gonorrhea would be.  Because of these facts, my advice to you is to go and get tested for both penile gonorrhea and chlamydia.  At this time, if your tests are negative, you can be very confident that you did not acquire these STIs which are the ones you are most at risk for.

Your risk for other STIs from this exposure is lower than for gonorrhea or chlamydia but there is still some risk for syphilis.  HIV is most unlikely- it sounds as though your partner was taking PREP and PREP is typically only given to persons who do not have HIV and is very effective for HIV prevention.  Putting these facts together makes it unlikely you were exposed to HIV.  So, what about syphilis?  Overall syphilis is a relatively rare infection and your partner sounds as though he is careful and tested regularly.  This all makes your risk for syphilis low., On the other hand, as a man who regularly has sex with other men however, your partner is among the group who is at relatively high risk for syphilis.  Were you to develop syphilis, you would most likely develop a penile sore in the three weeks after exposure.  If this does not happen, I would suggest a syphilis blood test about a month after this exposure to be 100% sure you were not infected but I would not worry too much about this possibility. 

To summarize then, I suspect your overall risk for STI from this exposure is quite low but not zero.  I would suggest getting a urine test for gonorrhea and chlamydia to rule out the statistically most likely (although still rare) STIs.  If these tests are negative you are almost certainly to be in the clear although to be completely sure, I would suggest watching for the appearance of genital lesions over the next few weeks and to get a syphilis blood test about a month after your exposure.  I would not be worried about herpes or test for it unless you develop lesions.  Once your tests for gonorrhea and chlamydia are negative you can resume sex with your GF with a high but not 100% certainty that you did not get an STI.  For that, I would want you to also have a negative syphilis blood test a month after the event as well.

I hope these comments are helpful.  EWH

Thanks for your thanks, 

Below is a calculation to illustrate why I said what I said to you.  The chance that your partner had gonorrhea, chlamydia or other STI is less than 10% and probably lower since he had negative tests about a week before you had sex with him.  The average risk for infection per exposure too  an infected partner is less than 20%.  20% of 10 is 2%.  The fact that you do not have symptoms makes the likelihood of infection, if anything, lower.  EWH

Thanks for correcting y misinterpretation.  Even with the larger dates, the risk is tiny.  To acquire syphilis in a little over a month would be most unusual.

I would not be worried if I were you.

This is our 4th interchange so we have exceeded the limit set by the Forum.  I hope these comments have been helpful to you.  This thread will be closed later today.  EWH