So my boyfriend and I have been dating for about a year. Right before we started dating he still had sexual intercourse with his previous ex (which I just found out today). And while he was still having sexual intercourse with her, he was also having it with me. At this time, I was experiencing weird symptoms and I actually thought I had chlamydia. So I got tested and the test came back negative. So I know I didn't have it back then. But my boyfriend also told me that around that time, maybe a little before, that his ex got a screen and didn't have any STDs. So how does he have chlamydia now? Did he have to have been cheating? Or is there a way he had it back then and still has it now? But I got screened then and I didn't have it.  Any help would be appreciated.