I know this is an old thread, and this is actually my first post here,

however, this thread is the first one I've read.....and I can relate 100%. so here I am!!
I'm glad our friend came out of it well, but the only thing to do in this situation is get a check up. The only reason I'm posting is that I know that feeling really well, and it's easily bad enough for someone to commit suicide, but there's no reason for that extreme, get tested!
I'm an old(ish) fart now but in my teens, and my early 20's and early 30's this was exactly what I went through. In the end I'm completely clean.
This happened once with a guy, and twice with gals. The first was with the owner of a sex shop when I was 17, it wasn't anal sex, but there was penetration, saliva and other juices involved - the owner of a sex shop

my panic was completely justified. Next was with a pretty rough chick. and because my little weapon does the talking and runs the show, I had no choice at all, I had to hit it being unsafe... The 3rd.............I lived in South Korea for 7 years and after a few years I was a fluent Korean speaker, and that helps to find the right places to go. Sex prices vary, anywhere from $25 to...well, the most I paid was $2k to smash, I shit you not, probably the hottest chick I've ever seen!! It was incredible. Oh, and I had her for the rest of the night, maybe 5ish hours, and I didn't close my eyes once!!
Anyway, the issue there was when I visited one night when the girls were busy, and the ajuma/halmoni (old lady running the joint) was in front of me telling me to wait, but there was a problem... she was carrying a really huge set of titties so I put it on her... She was over the moon so we went at it, without a condom, and then I rolled her over and turned her into a dog. That was when I saw her genital warts growing on her ass cheeks near her pussy. I remember thinking to myself, fuck it! I've probably already got it...and I just kept going, however, as you all know, things change after you blow your load, and that's when I started freaking out!! I understand the op's panic all to well, but I am a very lucky boy!!. Getting tested is the only thing to do. Let's say you hold off on the test because you're frightened of the result...but what are you going to do in future? Never have sex again, OR bang your next victory and possibly pass it on to them??
Let's say the unthinkable happened and you picked up HIV or...the first time you had sex... You never got tested and payed it forward. It could be passed on to anyone, your man's tweaker, for example, and he goes off and bangs 100 guys before he finds out himself,. and there you go - you're responsible for 1000 infections. They're all on you - could you carry that weight for the rest of your life?? That's a LOT of weight... Then, there's the next scenario - You met someone, you fall head-over-heals for them, but they want to hold off until your married. You do,. and you marry 6 months later. You bang away and then you've infected the person you would die for....Could you carry that weight for the rest of your life?? I can only try to imagine it, it's probably nowhere near as heavy as the real weight...
If you're freaking out, get tested at your first opportunity, and at least freak out over the right thing rather than freak out about every possible thing because that's what I did. Every waking moment, just spinning around in my head, that I've got every infection it might possible, and I'm never having unprotected sex ever again it sucked!.
If I help only one person with my post, that's plenty enough.
All the best.