Let's face it, you can catch a cold or flu from a stranger's sneeze on a bus and you can get food poisoning in a dodgy restaurant. You can't catch them from a toilet seat, but there's real pleasure involved in catching STIs.
Admit it. Ladies, you love your pork sausage and gentlemen, you love to wield that sausage. Sometimes you can both get so carried away that you just have to do it regardless and occasionally there are consequences from unprotected sexual shenanigans.
While it's up to both of you to take care, it's often the gentleman who takes the blame, although there's nothing to stop the lady from assisting the man to take precautions. In fact, it's quite a nice caring, sharing part of the procedure.
Oh! You forgot to slip one on? I just couldn't stop myself.
You don't like the feel of it? It just doesn't feel natural.
You were drunk at the time? Then how did you manage to get it up?
STIs: the pox, the clap, NSU or non-specific urethritis, chlamydia, pelvic inflammatory disease, they are all out there, and in certain parts of the world there is also a high risk of catching an incurable and deadly virus, you know what I mean - HIV. Of course, the most natural outcome of all is, let's spell it out - unwanted P-R-E-G-N-A-N-C-Y.
But an STI is nothing to be ashamed about; that is, until you find yourself in the "special", or what is, in medical parlance, known as the genito-urinary clinic. It's there when you find yourself stuck in the waiting room with a bunch of 15 year olds, fiddling with their i-phones and talking some strange gibberish version of English, that the reality kicks in and the thoughts run wild.
"What am I doing here with these grubby little tykes? I thought s/he was nice. How was I to know s/he's a walking sexual disease? Doesn't s/he have any symptoms?"
Being nice is not a prerequisite for being clear of STIs. In fact, it probably makes it more likely that your sexual partner will be popular with the opposite sex and will have plenty of opportunities open to him/her. Don't blame him/her for taking advantage of that.
Of course, if you manage to get into the swingers scene, it's an accepted risk, and I dare say that each member(!) is responsible for his/her health, but it's probably considered a proud achievement to catch a little something after a good workout.
So my advice is, don't be ashamed of your STI, be proud and think of it as an achievement. Just get it treated in a private consultation.