My 9 year relationship is hanging by a thread

My man and I have been together since we were 15 and 16. We got engaged in 2017. We had our son in 2020. We’ve been to hell and back together. This past Thursday (March 2nd), I went to see a doctor for a normal checkup/talk about medication. She said I was due for a chlamydia screening. I didn’t even think anything of it, because I have been with only one person my entire life, and they test you for STDs when you’re pregnant and I was clear then…they called me with my results and said I was positive for chlamydia. Obviously it was a shock to the heart for me. When I brought it up to him, he denied denied denied that anything ever happened with anyone. Of course I want to believe that he’d never betray me like that, but STIs do not just spontaneously appear, and I know FOR DAMN SURE where I stand. He’s a truck driver, and he said that the public showers he uses are unclean and that they can have unclean towels and that it would be possible that he picked something up from them. Is there even a slight chance that could happen?? I’m sick to my stomach, I lost my appetite, and I’m just extremely embarrassed. I NEVER thought I would be a “statistic.”

UPDATE: 3/9/23

He went and got tested. His results came back today and they were NEGATIVE! Make it make sense. I have only been with him my whole life. Medical mystery???