From wikipedia I got this:
In Brazil, the Dia dos Namorados (lit. “Day of the enamored”, or “Boyfriend’s/Girlfriend’s Day”) is celebrated on June 12, when couples exchange gifts, chocolates, cards and flower bouquets. This day was chosen probably because it is the day before the Saint Anthony’s day, known there as the marriage saint, when many single women perform popular rituals, called simpatias, in order to find a good husband or a boyfriend.