Given the sheer amount of stress that Tristan had been in after finding out that he had to get married by the end of the month or lose everything. He had held on to the foolish hope that by getting married on time everything would be resolved.
That in having an actual spouse all would fall into place and he would no longer have to worry about his position, but Zachariah had proven him wrong. His cousin's outburst at the restaurant was proof of that.
Like most people, Zachariah's drunk self, was more honest than his sober self, at least as honest as somebody like Zachariah could be. For him to come right out and threaten Tristan, telling him that he was going to end him, that meant that Zachariah had not given up that he still suspected. Had he bought into the whole story of Tristan meeting Ariel and then falling in love, Zachariah would have insulted Tristan. Probably even coming up with few choice words for Ariel.
