【题目】既然你已经知道这件事了，我就不想再谈了。

【答案】Now that you have already known the matter, I don't want to talk about it any more.
【解析】now that 固定短语“既然”；want to do固定短语“想要做......”；talk about固定短语“谈论”；not...any more固定短语“不再”，因此答案为Now that you have already known the matter, I don't want to talk about it any more.