Hello, I Am Writing Concerned I May Have Extracted Impetigo

Hello, I am writing concerned I may have extracted impetigo from my boyfriend during sex. We had unprotected sex about three weeks ago and he soon after found out he had impetigo. Now when we had the unprotected sex he had no sores or open wounds on his body other than his armpit and it was one tiny sore. I now have a black blotchy ring around my anus and I'm freaking out. What is this. It does not itch or burn or sting or hurt at all?