Not sure, this is a strange question. Are you accusing someone of giving you an STD? You can actually get free STD treatment and exams at many county hospitals. I am assuming you do not have insurance?
Seconly, if you caught the STD then you had unprotected sex with this person and unless you were a virgin when you met them, you ave no way of proving who gave it to you. If you had sex with them, you hold some responsibility for the STD. If I were them I would not sign the contract and just because they sign and notarize it, does not mean it will hold up in court.