People make mistakes, sometimes those mistakes have consequences. Whether or not someone deserves sympathy for their mistake is determined by how fitting that consequence is for that mistake.

For example, I forget to put on sunblock at the beach and I get a sunburn. That’s a proportional consequence. A mundane, annoying consequence for a mundane, dumb mistake.

Having unprotected sex is a mistake. But is the consequence of HIV, a potentially deadly disease, really proportional to that mistake? Maybe herpes or gonorrhea, but HIV/AIDS?

So if you don’t think it’s a fitting consequence, then yes, it does deserve sympathy. If you do think it’s a fitting consequence, then that’s an entirely different matter that I’ll argue, but from the text of your OP it doesn’t seem like that’s the case.