STD!!!

So, my boyfriend this past week and a half has gotten really sick we suspected kidney stones(by his symptoms) took him to the doctor they had him do a pee test and the results were chlamydia. (Back story, we’ve been together for over a year and I’m very much loyal to him) he Automatically blames me for cheating. I’ve never cheated on anyone and I really plan on marrying him so he looks it up and it said it could have been carried in my body without me knowing. He’s extremely pissed at me because I wasn’t a virgin when we meant(neither was he) so my question is how have we been together for over a year and all of a sudden he becomes ill and has it. Do you think he cheated on me?.... oh also he is extremely pissed because the gynecologist I went to was a guy... I don’t know what to do. I really need some advice from y’all!