I have an STD

I have been with my boyfriend for almost 6 months and the last time I was tested for STDS was in March 2018. I had some symptoms that looked like a UTI or Yeast Infection coming back for 5 weeks. I got tested again and I have chlamydia. When we got together, we decided to be exclusive and I really do believe him. I’m feeling really gross and dirty. I’ve only had sex with 3 people, the only options are that my boyfriend got it from someone before we got in a relationship and passed it to me, or my ex had it from cheating on me. How do I even go about this?!