I always thought that decision was taken when Mat tested Joline and Teslyn about the warning note he found in his pocket (that Elaida may try to kidnap Nynaeve and Elayne). He initially thought it was written by Joline, but she fails the test, so he goes to Teslyn to test her. Finding that she was the one, leads to his fateful decision to rescue the damane Aes Sedai, which in turn results in his surprise encounter with Tuon, her kidnapping and all that unfolded. Had he followed his hunch that Joline was the one, he'd probably never be in the palace or meet Tuon the night of the escape.

randfandom