The Shaytan is the Companion of the One Who turns away from Ar-Rahman

وَمَن يَعْشُ

(And whosoever Ya`shu (turns away blindly)) means, whoever willfully ignores and turns away

وَلَن يَنفَعَكُمُ الْيَوْمَ ('Since you were wrongdoers, it will never benefit you today that you are sharing the punishment with each other.'...43:39) There can be two explanations of this verse. One is that since your 'kufr' and 'shirk' (disbelief and ascribing partners to Allah) has been proved, your longing in the Hereafter in the words, "Will that this devil had been away from me," will be of no avail, because all of you will be sharing the same punishment.

The other explanation could be that after getting in Hell, your sharing the punishment with the devil will not benefit you. In this world, indeed it happens that when a few people share the same misfortune, everyone's burden of misery becomes somewhat lighter, but there in Hell, everybody will be so terrorized that nobody will be able to lighten another's misery and hence sharing of the punishment will be of no benefit. (The translation given above is based on this interpretation.)