I hate to beat on a dead horse, but I have been in a similar situation myself, the problem isn't necessarily weather or not you are actually having sex with the adult in question, because lets face it, how many of us are going to believe that that isn't the case? A court would likely see it as there being a sexual relationship, weather or not it actually exists. Now, technically speaking that if the two parties in question are not engaging in sexual relations (for the state of Wisconsin, sexual relations could mean so much as kissing) there really would be no way to prove weather or not you are actually having sex. For the sake of the court we have to assume that they are, and look no further. It's honestly a shi**y situation for the OP (well, actually for the girl in question) but unfortunately the law is what it is, and it is there for a reason. If the OP believes it should be modified, it would be my suggestion that he attempt to do that. But until the time that said law is changed, unfortunately OP, you will have to stick with girls your age (and it is very condescending to say that anyone in public education or in high school isn't on your level, as that is just an ignorant statement as I am sure you have not met everyone.) or wait until you are of legal consenting age.
Why not give other girls a chance?
(I am sorry if this has already been stated. Also, my apologies for posting on a necrothread)