【that people thought I was so angry or sad that I ended my life then】这个是主语从句,原句中用it形式主语代替了.
【I was so angry or sad that I ended my life then】这个是thought的宾语从句.
这里有个so that句型,可以把【that I ended my life then】理解为结果状语从句.
整句话的结构就是,【that people thought i was so angry or sad that i ended my life then】是主语,is 是谓语,useful是表语,to me是状语.
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