Chlamydia?!

I'm really stuck on how I got chlamydia. Because apparently you can only get if you've had sex with someone who had it, me and my boyfriend have been together for 3 years... Maybe he cheated... Or maybe it's a false positive. But like I said you can only get it if you had sex with someone who had it an that person could have only got it if they had sex with someone who had it... So how does it all start... Where does chlamydia actually come from...? Is it because of having a dirty vagina... The first person who ever got chlamydia couldn't have gotten it from someone else if they were the first .. Like do you see what I'm saying? Sorry I just overthink things. But I'm super confused because I've never cheated throughout our relationship and he was the one who took my virginity, so maybe he's had it for a while or he got it from someone else by cheating... If that's the case, all hell is going to break loose. He's going to get check tomorrow to see if he has it and if he doesn't then there's no way I can have it right?