Well...umm...
I take it that the picture you "accidentally sent" to the person who "stole[] [your] jeans" was pornographic in nature. While I have to wonder how it is that you "accidentally sent" such a picture and why you would send such a picture to anyone and how it is that this person had access to your jeans so as to steal them, I don't think any of that is really relevant to any legal issue.
It is a crime to threaten the publication of your photo as leverage to prevent you from going to the police or suing. However, I have a hard time believing that a pair of jeans is worth even the hassle of making a police report or filing a small claims action.
I suggest you re-evaluate what sorts of pictures you take or allow to be taken of yourself, along with disseminating such photos to others, and move on with your life.
Then make a report to the police and/or file a small claims suit. If you report the matter to the police, you're free also to mention the threats.
BTW, your 19yo (ex?) boyfriend doesn't have the ability to diagnose a medical condition based on a camera phone picture. If you're concerned about your health, see a doctor.