Wait, your ex connected pal nibbles on nibs? They are extremely bitter...so why?

Great chocolate quality is formed by the initial types of cacao (Caribe is generally considered top dog), the fine processing (i.e. conching, or roasting and turning, time) which produces silky smooth texture, as well as the adding of other ingredients.
The lower end products are usually conched very little or not at all, yielding a grainy, coarse texture, and may have imitation vanilla and other less pleasant ingredients added.

I have no idea which additive might cause someone's tongue to swell after eating cheap chocolate but the solution seems simple: buy only great chocolate and you'll probably be satisfied savoring eat a small yet intensely flavorful amount at the time. (Think a fine brandy vs a cheap beer)

Try Valrhona from France, often named the best in the world, it is preciously expensive but sublime. I'm at my happiest when I have an assortment of fragrant olive oils, good chocolates and a few nice wines tucked away in my pantry appropriate to whatever mood or menu tempts.