In the story, M+M, what does Martin remember about his part in bulling Mariela, and what is happening in the present time, as he remembers?

In his present moment, Martin and the rebels experience a siege of smoke bombs from the Colombian government. He then remembers how he helped the girls from Mariela’s class bully Mariela by leaving a used tampon on her chair with a note attached, reading “Fatty” (84).