why is the encounter between pedro and tita in "december" so significant? what happens to each of them?

Dr. Brown notices the heat and smell of the sexual attraction between Pedro and Tita and decides to leave the party. His departure saddens Tita but she is glad to have a chance to love Pedro freely.Tita and Pedro enter the dark room where they had met secretly many times before. As Tita tries to control her breathing to prevent this from happening, she realizes Pedro has already died atop her from lighting all of his matches at once.

Tita fears that without Pedro she will never again be able to light all of her matches at once and as a result will never be able to see Pedro again. She covers herself in her bedspread to block out a chill she has already begun to sense. Determined to light her candles, even non-traditionally, Tita swallows the box of candles John gave her the day before. As she chews the candles, Tita reminisces about her and Pedro in order to light the candles on fire. Soon enough Tita joins Pedro in the tunnel, and the two are joined eternally.

Tita and Pedro’s bodies spark and set fire to the bedspread, which then sets fire to the entire ranch.