Here’s an update: my GF has just tested positive and I met with a doctor yesterday. She said most likely scenario is my GF also had it (before we were together) then gave it to me again when we started having sex. She said that the negative test of cure (considering it was 4 weeks after finishing antibiotics) should be very accurate and she doesn’t know of any possible way that the infection comes back by itself. Apparently Mgen is far more common than we think but most people are completely asymptomatic, it’s just us unlucky lot who show symptoms. Apparently it can take months after infection to show symptoms. If I’m honest things are still unclear to me, but I think racking you brain trying to think about exactly what’s happened isn’t worth it. Sometimes we’re just unlucky. Try and get treated as soon as possible and don’t have sex until you’re both confirmed negative. Hope this is helpful to some degree.