you were exposed to chlamydia from one of your sexual partners but it would not be possible to know who or when you were exposed. yes chlamydia can go unnoticed especially in women for a long time. not all sexual partners are 100% honest about their fidelity in a relationship. as you know using a condom would have prevented exposure. make sure that both of you are treated and test negative again. since you do not know for sure that your current partner exposed you it would be best to not have unprotected sex.
can you get chlamydia by having with the same partner for years? can people have chlyamdia without notice for a years?