Sugar certainly is addictive in a physical sense. Read David Gillespie Sweet Poison/ Sweet Poison Quit Plan and watch Robert Lustig's lectures on sugar on youtube. Basically there's no "off switch" for fructose... most foods have a feedback mechanism whereby once your body has sensed it's had enough, it sends back appetite hormones to dull your appetite. Not so with fructose, we're evolutionarily programmed to eat as much as we can, eg gorging on autumnal fruit to survive the barren winter months.
As regards to psychology, it's probably a bit more nuanced, but Robert Lustig goes into this in his book the Hacking of the American Mind, which is about the contrast between dopamine and serotonin, and pleasure and happiness, respectively. Sugar very much fires up the dopamine and pleasure reward circuits, leading to addiction pathways.
I think though where your therapist is coming from is that if you've got a history of eating disorders and addiction, then cutting out food groups could shift those underlying behaviour patterns into orthorexia.
My retort to that though would be that sugar isn't a food group. There's essential amino acids and there's essential fatty acids; starchy food can be a useful boost to energy intake, and can be a vehicle for vitamins & minerals, but is not essential. And fructose (50% component of table sugar & in most processed foods) is a turbo charged carb. Eat real food (meat, fish, vegetables, dairy, eggs, olive oil etc)... avoid processed... cook from scratch, and only eat sweet stuff if it's in the form of whole fresh fruit (ie its fibre is intact, which slows & mitigates fructose absorption).