Is my boyfriend cheating?

Long story short, me and my boyfriend have been together for two years and i just tested positive for chlamydia. I tested negative two years ago when we first got together but had already had unprotected sex a few times. I have not been with anyone else during our relationship. Is it possible he or me got it from a past relationship and it just was dormant or wasn’t detected on my first test or is he most definitely cheating on me?