Straight to my encounters (all similar): 

Since June 4th up until yesterday, I've been meeting other male partners for mutual masturbation and oral. Total number of partners since then is 13. Prior to any sexual activity, I always ask about HIV status and frequency of testing: All 13 were HIV negative, and did indeed test frequently (some were on PrEP, but not all). These men were also bisexual, but either married, closeted, or just curious and experimenting. I have no reason to believe any were untruthful with me, but risk assessment is always handy to have. No anal whatsoever with any. 

On one occassion only, there was mutual oral between myself and a partner, but that was it. 

I know from previous and similar threads that mutual masturbation is no risk, and that receptive oral is no/low risk, but I'd appreciate an assessment nontheless and check whether to test or not. 

My last complete STI test was on June 28th, neg and clear for everything. No symptoms or discomfort of any kind so far. 

Many thanks, as always.

I agree with what you have already learned from your previous three questions and reviewing other discussion on the forum -- that mutual masturbation carries no risk of HIV transmission, and that receptive oral sex (you performing oral on another male) is low risk. But not zero:  CDC estimates roughly one chance in 10,000 of being infected, if the penile partner has HIV. In the opposite direction -- i.e. insertive oral, i.e. your penis in your partner's mouth -- the risk is very close to zero; no HIV transmissions have ever been scientifically documented, and CDC estimates a risk of one in 20,000. 

Should you be tested for HIV? There are two reasonable perspectives. First, from your description of the sexual exposures you have had, there is no need; there is virtually no chance you have HIV. Second, however, is that since you are obviously nervous about perhaps being infected (otherwise you wouldn't be here asking this question!), you probably should be tested for reassurance. A negative test result likely would be more reassuring than anything I can say. And for what it's worth, I'm surprised to hear you were tested for STIs a few weeks ago, but not HIV. Why not? 99% of people worried enough about STIs would be tested for HIV. So for reassurance purposes, I suggest you do it.

I hope these comments are helpful. Let me know if anything isn't clear. (By the way, this is your 4th question on the forum, but under two different usernames. It's not a big deal, but is against forum guidelines. For future questions, please stick with one or the other!

Best regards--  HHH, MD

The tests I did on June 28th did indeed include the combo HIV test as well, and syphillis, hepatitis, etc. Neg for all, should have clarified, apologies.

I'll ask the forum administrator to remind you the two different usernames/accounts. She might merge them or delete one. (To not risk confidentiality issues, I won't remind you of the separate usernames.)

Regarding condom use, I am consistent user with both females and males, and insist on it. When the condom doesn't break and is consistently and correctly used, is it accurate to say protection is 100%?

Can you please explain and elaborate on human error/effectiveness vs. biological effectiveness? I know it's one subject per post, so apologies to deviate.

And thanks for the discretion and privacy with the account details, appreciate it.

The words you use pretty much tell the story about biological versus use effectiveness. Biological has to do with the possibility an infection can pass through or get around a barrier. Nothing can pass through latex, polyurethane, and probably natural membrane condoms (despite confusion about the last online and elsewhere). For STIs transmitted skin to skin, usually there is contact above the condom, and fluids might work their way part way down the penis above the condom rim. Hence biological effectiveness is close to 100% for STIs transmitted by fluids (gonorrhea, chlamydia, HIV) and probably around 80-90% for most skin to skin infections (syphilis, HSV, HPV, MPV). Use effectiveness takes into account exactly what you mention, i.e. human error and also includes condom breakage. Misuse can be things like partial unprotected sex followed by condom only for ejaculation, simple forgetfulness, and so on. Therefore, even when biological effectiveness is close to 100%, regular condom users do not have zero risk of infection. Obviously, the more observant and careful you are, the closer your own use effectiveness comes to biological effectiveness. But it's rarely or never 100% protection.

That completes the two follow-up exchanges included with each question and so ends this thread. I hope the discussion has been helpful. Best wishes and stay safe.