Chlamydia positive, partner negative

I recently tested positive for Chlamydia. I took my antibiotics and everything should be fine now. However, my sexual partner (long term) had a negative result (and so did the guy before him because the condom slipped off). I’m confused on why I had it and not them. My doctor said that a man’s body can get rid of the infection without needing the treatment. It just doesn’t make sense to me and now I’m left not knowing who transferred it to me, although my symptoms didn’t start until after I had sex with my long term sexual partner after not seeing him for a month.