Is it libel if I don't mention the name and identify our city?

Yes, you can report facts on a blog. Keeping the other person's identity a secret is a good idea but you'll want to go beyond leaving out his name and address. Avoid any kind of physical description or regular activities that would give a clue about his identity. There are several popular female authors who successfully write about their ex's in columns, blogs, and books. Take a cue from them on how to refer to a former relationship.

It would be nearly impossible to win a lawsuit claiming a particular person passed HPV to you, since you would have to prove you did not have it before and that you had no other sources of possible infection. You can say this is so, and a jury could weigh that testimony, but it is not very strong evidence. HPV can linger for many years, most people get it without even knowing they have it, most HPV goes away on its own, and some turns to cancer. The type that causes warts is not the kind that causes cancer. Further, it would be nearly impossible to prove an infected partner was negligent in transmitting the virus to you, since the type of HPV that causes cancer usually has no symptoms. Therefore, you are most likely spending money on a lawsuit with very little likelihood of you getting anything out of it, other than embarrassing yourself publicly on the record as having an STD. Is this something you should write about in a blog? Of course not. Posting that this former lover of yours had an STD is defamation per se, which means he can bring a lawsuit and you will be the one who will have to prove that what you are saying is "true," which you will not be able to do, for all the reasons you will not be able to do so in the other lawsuit. And with defamation per se, the plaintiff does not have to prove damages, because the statements alone are considered so damaging.