You'd only have grounds to press charges IF you can show that he knew that he was HIV positive but knowing it, failed to either tell you or at least use reasonable precautions (e.g. condoms). If he did not know when he slept with you, he did nothing wrong (he can't tell you what he did not know); if he did know but always used condoms, then what he did would most likely not be considered criminal (his "intent" would not be sufficiently reckless or bad to be considered a criminal act), since he took precautions--but in this case, if you were in fact infected, you could likely sue him for having infected you. (That is because the conduct which supports suing someone is not as "bad" as what is needed to convict them of a crime, the same way that many people who drive carelessly and get into an accident can be sued but don't go to jail; you can show a level of lack of care--not telling you--that supports civil liability, but not criminal.)