But HE is the one who abused you and totally fucked you over, not her. She may be an asshole, but he completely disrespected and devalued you. Can't you see that? He is untrustworthy and shouldn't be excused for his behavior. Why in the world would you even remotely think about being sexual with him again? HE LIED TO YOU. About something extremely, crucially important. The fact that a guy like that could be domming anyone is another reason why I find the whole D/s scene distasteful -- seems like there should be a test you should pass or an apprenticeship to undergo before being allowed to do it.
But you need to find a way to gather up all your sense of self-worth and look at this objectively, as if a good, close friend were in your position. What would you say to her? "Oh, no big deal, she's a nutty bitch and he was polite at lunch, so what if you get infected with STDs and STIs? So what if you didn't have all the facts about what risks he was taking? He's the dom, he is in charge. So, why not keep putting yourself in the position of doormat? I mean, you're submissive, right?" Wrong.
Have a little self-respect, hon. This guy doesn't deserve you.
Oh, and have you scheduled an appointment to get tested yet?