It has been a long time forming.

这种状况的形成历经了蛮长的一段时间。

It has been a long time since we met.

这是一个很长的时间，因为我们满足。

It has been a long time since we last met.

自从我们上次分别已经有很长时间了。

It has been a long time since last came here.

自从我上次来这里有很长了。

It has been a long time since I last came here.

自从我上次来这里已经有很长时间了。