Please respond

Hey, I’m 25 years old. I recently lost my virginity to my boyfriend we were dating for 5 months and made it official in October . He gave me a STD and said it was from a previous partner before we committed to each other.He still is in contact with her after the fact. I told him it hurt my feelings that he was still talking to her. I gave him an ultimatum about the situation.basically to stop talking to her but it continued. I finally broke up with him and I’m not answering any calls and text. Am I overreacting? I just feel like they have something going on. I’m so hurt about the situation and advice??I feel I had no one else to talk to.