HELP: Chlamydia positive 3 year relationship

My partner and I have been together for 3 years. Last year I was pregnant and tested for chlamydia and it was negative. I was tested again before baby arrived. Negative again. I’m assuming I got it around 5-7 months postpartum because that’s when the symptoms started. I told my partner when I tested positive and my partner told me he didn’t cheat on me and he must have gotten it from the girl he dated before me. Tell me, would it be at all possible for this to be true?

We used the FAM method of birth control before we started trying to get pregnant. Which means we didn’t use condoms.

Is it possible to have unprotected sex for 3 years without me catching chlamydia or is he just a straight fucking liar? I tried to google but I can’t find a specific answer to this question.