I'll be happy to chime in here; I hadn't noticed this thread earlier.
I used condoms for many years (for anal sex only - I have always done oral bare, because what's the point of doing it at all otherwise?), then did some judicious barebacking (mostly as a top) during the '90s. Now I'm on PrEP and bareback essentially all the time.
During all of this, I've had crabs, gonorrhea, and chlamydia each a handful of times, and a couple of bouts with non-specific urethritis and syphilis. All happily cured with antibiotics. Yep, these are a pain in the butt (and when you're getting three rounds of penicillin injections, that's quite literal!). What's the worst part about it? The ones that are really hard to notice. Specifically, chlamydia (very mild symptoms penile, no symptoms at all anal) and syphilis (if you miss seeing the chancre, you're shit out of luck until it hits secondary, which doesn't happen for months and can be a mild skin rash easily mistaken for something else like a detergent allergy). Those friends of yours who claim they never catch anything are probably full of shit. In the bottom's case, likely it's shit full of chlamydia and gonorrhea at least. Which explains a lot about why these things are so prevalent...
I try to get tested every three months, though sometimes it winds up being more like six (visiting the doctor is always more of a production than it ought to be). That means if I pick one up and don't notice it, I often have a fair number of actual buddies to contact with bad news.
Apparently some people find this upsetting (my boyfriend was appalled when I told him last month that I had chlamydia) or embarrassing (OK, I find it mildly so, but not really all that much). But honestly, it shouldn't be - all of these are not particularly strange or unusual to encounter if one is having what I would call a healthy sex life. Communicable diseases are... contagious, how surprising! 🙂
As far as prevention goes, doxycycline can be used as prophylaxis against syphilis, and a number of studies have proven it to be effective used in this way against both syphilis and chlamydia... which incidentally are among the hardest to notice STIs. Because it's a broad-spectrum antibiotic with a lot of other uses, I don't find it appropriate to use all the time, but for occasional rounds of abject piggery at the sex club (which for me are altogether too rare), I think it can be helpful. A Google search will give you many links to the actual studies if you're interested.
Also in the way of prevention (though I don't have any studies to cite) I have heard that simply cleaning up well after exposure can reduce rates of transmission. From what I know of anatomy, if you're having receptive anal, that's probably a lost cause (and obviously it is if you like keeping cum inside to absorb 😈). If you're a top, on the other hand, it's easy (and I think probably worthwhile) to give your dick a wash *soon* after whoring it around, and to drink lots of fluids so the inside gets washed. It may be worth drinking cranberry juice (the theory is that the sugars in cranberry juice are excreted in the urine and inhibit some bacteria from sticking to the mucous membrane in the urethra, but I don't know of any hard evidence backing it up), or taking hexamethylenetetramine (which is excreted in the urine, where it is converted to formaldehyde that acts as an antiseptic, as explained on Wikipedia - here's a link to the branded product that contains it [think before following links] https://www.amazon.com/dp/B01C8BR84O ).
That said, all of those strategies haven't completely prevented me from crossing paths with a thing or two. So peace out, pig out, test early, test often!