How does a pimple go away on its own, like what happens to the pus inside the pimple?

It probably squeezes out on it’s own.

You did not show us the image of the burger, but i shall try to answer as best i can.  when purchasing food, always consider the ingredients as well as the person who prepared it. consider if they were hygienic people or not, in case the burger was infected with bacteria. no mortal should place an infected burger into their mouth.