一句英语的理解

I think在这里是插入语，与I think that he thought that my failure was his fault.即he thought that my failure was his fault是I think的内容。翻译成：我认为，他觉得我的失败是因为他的错误。

I think （插句或句尾） “是...罢”。

按原来的意思呀，
只不是插入语，没有特别的含义

我想,他以为我18岁了,而我的失败是他的责任.(仅供参考)

我认为或者我觉得

I think在这里是作为一个插入语，并没有什么实际意思，就譬如She is good at English I think and in fact she is.中一样没实际意思。原句去掉I think来理解，即为： was eighteen years old, and he thought, that my failure was his fault.