I am a lawyer and let me tell you that despite the level of anger you feel over this issue, it would be almost impossible to win. There is no solid law that would provide grounds for your lawsuit but the Courts are being very careful about these and related issues so that they do not create a flood of lawsuits from every second member of public. I guess, theoretically you can win it based on the existing laws but you have to have the most brillian lawyer you can afford to fight this case.
: Well, depends...you should talk to a lawyer : some judges would place an equal amount of blame on you, because it's your job to protect yourself, and unless given proof you should assume that the person your with is infected with something, and you need to protect yourself. : But some would place all the blame on him for not informing you that he had herpes. : The best thing to do would be to contact a lawyer and find out what if any action you can take against him.