You are excused.

People enter into your life to leave.
Temporal.
Defined-
By the limitations of time.

The purpose they have to serve is theirs.
The purposes I have are mine.
Such, as accordingly.
Private, yet pervasively.

Some people leave and return.
Yet they will leave again. 

Undoubtedly, they will.

For between the two of us,
I think I too, may once have left.