How do you say have bin away for such a long time In french?

There are a few ways to say "I have been away for such a long time" in French, depending on the context and level of formality:

Formal:

* J'ai été absent(e) pendant si longtemps. (I have been absent for such a long time.)

* Je suis absent(e) depuis si longtemps. (I have been away for such a long time.)

Informal:

* Ça fait tellement longtemps que je suis parti(e). (It's been so long since I left.)

* Je n'ai pas été là depuis si longtemps. (I haven't been here for such a long time.)

* Je suis parti(e) depuis un bail. (I've been gone for a while.)

You can also use a more specific expression depending on the reason for being away:

* J'ai été en voyage pendant si longtemps. (I've been traveling for such a long time.)

* J'étais malade pendant si longtemps. (I was sick for such a long time.)

Remember to replace "absent(e)" with the appropriate gender for the speaker.