The question is bordered on ethics, life and technology. There is no cure for this kind of situation, as is there no cure for human errors. And there is no cure for virus (other than your immune system), so there is no cure for AIDS, not yet. Prevention is the best option. So go ahead have the blood of your partner right just before the holy moment (do not insert it yet), send it by FedEX to the lab, get it analyzed, read the report and if the report says '-', get your (or your partner's) stuff in. Or if you have to go through all this, it maybe just wiser to find another partner!