ever since 和since 还有since then 有什么区别?

ever since 作为连词=since 完成时态---- ever since +主+动词简单过去式
例：I have known him ever since he was a child.
他从小我就认识他了.
这种用法同since 差不多,不过 ever since 比 since 用得少.
再如：We have lived in Shanghai ever since we came to China.(自从我们来到中国之后就住在上海.)
then本身是个过去的时间点,since then表示从那个时间点到现在的情况,一般是现在完成时.
比如 I have not gone there since then.