First off, I'd ask what kind of bread you are eating. If it is wheat bread (even sprouted) you are exposing yourself to exorphins (morphine-like compounds) that, in certain individuals, and in certain individuals more than others, make bread an addictive food.
I recommend reading this interesting research paper "Opioid Peptides Derived from Food Proteins:The Exorphins"
Second, I'd recommend ditching the "jam jelly" for a whole fruit such as sliced banana or strawberries. Even if the product you are using is "made with real fruit" it is still a highly concentrated form of sugar and as such allows a large quantity to be consumed in a short amount of time. There is also research to suggest that sugar consumption (at least in rats) is addictive.
"Hoebel has shown that rats eating large amounts of sugar when hungry, a phenomenon he describes as sugar-bingeing, undergo neurochemical changes in the brain that appear to mimic those produced by substances of abuse, including cocaine, morphine and nicotine."
The third, and possibly most important element, is that of the psychology of bingeing. As a recovering binge-eater myself, I can relate to this part of your post..."I'm now in the cyclic mind set of oh, the day is already ruined, I might as well get all take advantage." In my experience, this thought follows a period of over-restriction. If this is the case with you as well, I would suspect that your "normal" eating habits also need to be considered as a factor contributing to an eventual binge.
To speak more directly to the question of "how to stop!", I would say that if you are in the middle of an episode, do something to change your environment or situation. For example, get outside and go for a walk, call a friend, etc. This can help you create some psychological space.
I also recommend that whatever the outcome (you eat yourself into a food coma or you do in fact pump the brakes and halt the bingeing episode) remain cognizant of the primary attribution error.
Essentially, this means that you will have the tendency to blame yourself for "failing" to stick to your diet, not having enough "willpower", etc. The truth is much more complex than that. There are factors of environment (both internal and external) as well as psychological needs (such as the need for autonomy/control) that are playing out. These have nothing to do with who you are as a person, however, and to change the outcome (your behavior) all you really need to do is to focus on how you can shift the environment in your favor (eliminating foods with the tendency to cause a binge, such as bread and sugar, managing stress, ensuring that your "regular" diet is providing enough calories or flexibility so that you don't feel restricted in the first place, etc.)
Hope this helps.