He even went as far as to accuse me of betraying him.
简单理解：as to accuse me of betraying him，不定式作结果状语。第一个 as 表示 far 的程度，才有了不定式这个结果。

基本结构是：as ... as to... ，它是 so ... as to .. 的变式，可以相等。不定式作结果状语。

又如：
We have got so/as plenty of food as to treat our guests.
我们有如此充裕的食物来招待我们的客人。

I'm not so/as stupid as to believe that. 
我还不至于傻得连那样的话都相信。
《牛津词典》

He even went as far as to accuse me of betraying him. 

【翻译】他甚至到了指责我背叛他的程度。

本句，go 其实是一个抽象意义的动词，go far 表示 “人的行为到达了很远很深的程度”。然后用 as...as... 作比较，用不定式说明达到具体的程度，即结果。