It was because of a carnival. That in another town. You wish you 2 never had gone there. It wasn't even much of one. But your boyfriend's interest was caught by the Mythical Creatures exhibits. You looked at them all. You were both pretty sure all the creatures were fake of course; no matter how real they looked. While you two were looking at the 'creatures' your boyfriend yelled out "Ow!" You asked what happened & he said rubbing his arm that it was nothing. Much later he excused himself to the bathroom inside the school the carnival was being held at. He looked like he might puke & looked a bit pale. The carnival was on the back lot of the school btw. After a few minutes you became concerned because he hadn't returned. So you went to find him. You headed to the boys restroom & as you neared it you heard your boyfriend groaning in what sounded like pain. "You alright?" You asked concerned. No answer. You headed into the restroom. You saw your boyfriend naked standing panting as if in pain & his clothes, socks & shoes were scattered about. Before you could say anything he seemed to seize up in pain and you began hearing cracks, pops crunches. You saw his toes fuse together into 3 as black claws developed on them. His fingers fused into 3 as they developed black claws too. His skin started turning purple & smooth like scales; losing his belly button & nipples. He dropped to his hands & knees on the floor as he started shrinking. Suddenly he grabbed his head & literally tore his hair out making him bald yelling "Brain hurts! Every hurts!" You saw his ears disappear becoming earholes. "B...ra...i...n h...urt...s..." He again cried out holding his head as his face started pushing out to a snout reshaping his head. "H...urt...s..." He cried out again as something white & small spilled out of his mouth. You saw a tail snake it's way out of his backside. You even caught sight of his penis & balls pulling up into him. "Kobold...hu..r..." He yelled out one final time & he collapsed on the floor. You ran over to him finally breaking from your trance & checked on him. You could tell he was alive because you could see him breathing through his agape reptile mouth which was full of sharp teeth. You picked up the purple anthromorphic reptilian your boyfriend had become. You by your best visual estimate he was about 2 ft tall now. You awkwardly opened your coat and stop them in there hugging him trying to close it to hide him. You think you managed it pretty well. You took him to the car & placed him into the passenger seat. You got in yourself & you were off. You were glad it was night because that might hide him better. After an hour into the drive he woke up. He startled you asking in a much different sounding voice than you knew "Where we?" You answered "On the road. On the way to my place." "Our home?" He asked seeming puzzled. You thought for a sec "Yes." There was silence again for awhile. You finally asked "You ok?" He answered "Am now." Questioning "What do you remember?" He answered after a few "Turning into kobold. Ko...lod..." At least he didn't have amnesia. "Sorry I left you clothes behind." "Kobold no need them. Kobold fine as kobold is now." Puzzled finally catching it "Why you talking like that?" He replied "Me no smart now." Concerned you asked "You lost intelligence?" He seemed to struggle with his answer "Me no smart now. Me not know word use." Well your boyfriend was a 2 foot tall purple kobold now. After getting home & letting him inside he headed off to the bathroom. You didn't know why though. A few minutes later he yelled "Bath for you ready!" Confused you headed to the bathroom to see indeed he had run a bath for you. And he was standing there too. You thanked him & you got in. Throughout the next few days he kept doing stuff for you. You questioned why he doing all that. "Kobold serves." You asked "Why you want to serve me? Why [his name]? And why you calling your kobold? I know you are one but still why." He responded with "Name too hard now. Kobold better mistress." "I not you master." This seemed to upset him. "Kobold serves. Serve mistress." You sighed "Is this what you really want?" The purple kobold nodded. "Fine." You answered sighing. Much later that night... You were starting to get undressed when the kobold entered the room. "Need help?" He questioned. "No. But I prefer privacy." The kobold asked confused "Why?" You didn't answer. "Why stop?" You didn't answer. "Mistress no need cover body." "What?" You asked puzzled. "Me no wear stuff." The kobold answered. It was true. The kobold wore nothing at all; being nude 24/7. You hadn't even thought about it because he is clearly an animal. "You know you right. Why should I care to wear anything around you." You said with a smile & you continue to undress. "Are you happy as a kobold?" You asked the kobold curious. "Me happy." He answered.
Boy this has been an adjustment for both of you so far.