Like the Marquise de Merteuil, the Vicomte de Valmont is in it for the game. Or at least, he professes to be, and he styles himself as a player, without any belief or trust in love.
Valmont employs a repetition, or parody, of other writers' styles throughout his writing. As he seduces her, the Présidente de Tourvel's religious tones begin to appear in his letters. The Vicomte adopts the Présidente's language in order to convince her, but this also tends to alter what he says. Therefore, he must subvert Tourvel's religious motifs to his own purpose with parody, just as he must subvert her religious convictions.
But Valmont's pride is also his downfall. So impressed by his former immunity to love, he cannot admit to himself that he has found a source of happiness in the Présidente de Tourvel. He is unable to allow himself to see that the game is over, and so he sacrifices the Présidente to the dictates of intrigue, and ruins himself as he has ruined so many women before.