Terry in the show probably has some body dysmorphia/eating disorders. He's been shown to have difficulty controlling his food intake with the nibs, the weird dieting with Gina and Amy and he's also used the gym to avoid his problems. Plus he had some PTSD in the early seasons (I think from shooting an innocent person? I don't remember exactly why) which is why he wasn't in the field for the first few seasons. Also I think technically his rank is lieutenant so I'm not sure he's technically a detective