Love and trust

Hey ladies , I just feel so lost and lonely in my situation right now and don’t know who else to talk to. Me and my boyfriend have been together for about 3 years now and since I have known him I have known him to be very loving and protective of me but also very insecure at the same time when it comes to me and other guys. I am a very nice and friendly person by nature and sometimes guys take my kindness for flirtation and my boyfriend says he lost trust in me when we had a job together about 2 years ago and he saw one of my coworkers messing with me and I laughed it off instead of getting serious and telling him to piss off. In retrospect, I see how my boyfriend could have seen the transaction and took it for more than what it actually was but I know myself and I know I wasn’t trying to be flirtatious with anyone, just a friendly coworker not trying to cause tension in the workplace, yet that’s exactly what I did and in my relationship too🤦🏾‍♀️ anyways recently over the past several months my boyfriend has been building this gut feeling that I slept with one of his friends and despite how many times he asks for the truth and I tell him I wouldn’t do that to him he calls me a liar and demands THE TRUTH or he is leaving. To put a cherry on top of everything I had test results come back from my GYN appointment saying I was positive for chlamydia! HOW? When I have only been with one sexual partner for 3 years?? 😭 AND he tested negative so he is convinced that I cheated for sure now, and I have no way to explain to him what is happening to me/us. He is ready to leave me over things I never even did , I feel like my world and future is falling apart right now. Any words of encouragement/advice? *To give you an understanding of where his insecurities may be coming from he was actually cheated on in the past after a 6 year relationship*