I was just in a relation with another guy and being the insertive (TOP), I was playing with my partner's anus with no condom until one point on the spur of the moment, it went all the way in, but around 5 seconds later I took it off and this was just once. We never had actual sex and this one insertion was the most contact we had. I asked if he was clean and on prep and he said he was. I don't know if I can trust him though because I don't know him that well.
I'm clean but NOT on prep. I'd like to know if I should look for PEP or if I don't have a chance of being contaminated.
Thanks in advance.
Based on the circumstances you are describing I can tell you that you are at pretty much zero risk of acquiring HIV from this encounter. Here's why:
(1) HIV is transmitted primarily through blood, semen, and vaginal fluids. Insertive partners (or tops) are at significantly less risk of coming into contact with these fluids, and to have them make their way into the urethra (https://www.poz.com/article/HIV-risk-25382-5829). Sure it is not impossible for a top to acquire HIV. But for anal sex, he would have to bleed into your urethra for you to be at risk. Blood does not have to be a part of anal sex, and if it is, it's going to take some vigorous fucking to get the blood inside you. Just a five second dip in the butt isn't going to do it.
(2) Your partner said he was on PrEP. Assuming that is accurate, and he was taking it as prescribed, then his own chances of having HIV are pretty much zero.
(3) I understand your point about not knowing if you can trust your partner. That underscores the point of PrEP: It protects the person who is using it. It is not up to you partners to protect you from HIV, that is your responsibility. If you enjoy condomless intimacy for sex, as many of us do, then you may find out how and where you access PrEP for yourself so you can have anal sex with or without condoms and still be protected from HIV. The Global PrEPME provider directory offers many resources around the world: https://www.pleaseprepme.global/prepme-map/
On a final note, I'd like to invite to encourage how some of your words may unintentionally hurt others. You may not have meant this, but referring to someone who is HIV negative as "clean" infers that people living with HIV are "dirty." That is generally considered an insensitive and hurtful stigmatization of another's body. It is less likely to illicit the kind of honest answers and clear communication that you are asking for in your sexual partners.
The same applies to the word "contaminated." People living with HIV have a virus. They are not diseased, they are not evil, they are not scary. If someone living with HIV takes their meds as prescribed then they will very likely have an undetectable viral load and therefore cannot transmit HIV to you or anyone else (https://www.preventionaccess.org/). You are less likely to acquire HIV from someone who is undetectable than from someone who tells you he is HIV negative but may not truly know his current status.
Of course PrEP takes away the need to have that kind of conversation at all. When someone is taking PrEP as prescribed their risk of acquiring HIV are nearly zero. So that takes out the need to "trust" anyone about their HIV status. Positive or negative, you still have full control of your body. This is true whether you top for 5 seconds, 5 minutes, or bottom for 5 hours.
To learn more about PrEP, check out our resource page here at The Body at http://www.thebody.com/index/treat/tenofovir_prevention.html.
I hope this information helps you to relax, and enjoy the sexual connections and intimate pleasures you so richly deserve.