Long time no see. 好久不见。

It’s been a while. 有一段时间没见了。

It’s been a long time. 很久没见了。

It’s been such a long time. 好久不见。

It’s been too long. 太久没见了。

I’m so happy to see you again. 很开心再次见到你。

Wow, it’s so good to see you again! 哇，再次见到你真高兴。

What have you been up to? 最近在干嘛呢？