In the grand scheme of things a crunchie isn't the end of the world, but you need to get your head in gear, the first 6 months will see your biggest weight lose stage, after 6 months things slow down and most people start to stabilise at a year post op, so you need to re educate yourself towards a healthier life style and get your head around eating properly as this will carry you through 6 month post and onwards.
It is entirely possible that you may never dump, i dont dump either and can and do eat what ever i want, though take heed when i say 'whatever' as i know and understand what i'm putting in my mouth, the calories involved and and what its going to do to me.
Chocolate is considered negative calories, it gives you nothing nutricious at all and only bad things, its a slider food also so should not be giving you any sort of restriction either.
Sorry didn't want to beat you up over this, but like everyone else here has said you need to get a hang of this, longer term there's no reason why you cant have the odd treat, i do myself quite oftern, but at your stage you need to be focussing on your food and eating properly.