What does the "both" in the second verse apply to if this is not the case?
Both clearly refers to Satan himself and (any) the (human) person whom follows his "order or whispering" of "Disbelieve"!
So as @Uma said both betrayer and the betrayed will be in end in Jahannam.
Now to your other questions:
To answer these we must go back a few verses starting by verse (59:11):
In qtafsir (a summary of tafsir ibn Kathir) this section (59:11-17) was entitled:
The False Promise of Support the Hypocrites gave to the Jews (Read in detail here and here)
Here some brief comments on the verses:
- Have you not considered those who practice hypocrisy, saying to their brothers who have disbelieved among the People of the Scripture, "If you are expelled, we will surely leave with you, and we will not obey, in regard to you, anyone - ever; and if you are fought, we will surely aid you." But Allah testifies that they are liars. (59:11)
This verse refers to the hypocrites, `Abdullah bin Ubayy and his like, whom sent a messenger to (the jewish tribe of) Bani An-Nadir promising them help. But this promise was a lie as they never intended to fulfill it.
- If they are expelled, they will not leave with them, and if they are fought, they will not aid them. And [even] if they should aid them, they will surely turn their backs; then [thereafter] they will not be aided. (59:12)
This verse just counts some of their (false) promises.
- You [believers] are more fearful within their breasts than Allah . That is because they are a people who do not understand. (59:13)
This verse shows that the hypocrites fear the believer more than Allah their Creator also read verse (4:77) and the description of hypocrites.
- They will not fight you all except within fortified cities or from behind walls. Their violence among themselves is severe. You think they are together, but their hearts are diverse. That is because they are a people who do not reason. (59:14)
This verse describes the fear and recreancy of hypocrites.
- [Theirs is] like the example of those shortly before them: they tasted the bad consequence of their affair, and they will have a painful punishment. (59:15)
This verse seems to be a link to the Jewish tribe of banu Qaynuqa' and what happened to them due to their betray.
- [The hypocrites are] like the example of Satan when he says to man, "Disbelieve." But when he disbelieves, he says, "Indeed, I am disassociated from you. Indeed, I fear Allah , Lord of the worlds." (59:16)
Now we see that the precedent verses are related, as the deception of the Jews by the hypocrites is compared or set likewise to the example of Satan and his whispering as the devil lures mankind into disbelief and when they obey him, he disowns them and declares himself free of their actions, saying:
I fear Allah , Lord of the worlds
so Satan has betrayed those whom he had encouraged to disbelieve (before) and left them out in the rain saying that he believe in God! It seems you've misinterpreted this verse. Also read in this context (14:22), where Satan on the day of Judgement says to those he betrayed:
"Indeed, Allah had promised you the promise of truth. And I promised you, but I betrayed you. But I had no authority over you except that I invited you, and you responded to me. So do not blame me; but blame yourselves. I cannot be called to your aid, nor can you be called to my aid. Indeed, I deny your association of me [with Allah ] before. Indeed, for the wrongdoers is a painful punishment."
So maybe this verse makes clear that the promises of the hypocrites and the promises of Satan are of the same kind... false promises!
- So the outcome for both of them is that they will be in the Fire, abiding eternally therein. And that is the recompense of the wrong-doers. (59:17)
This basically is answered and explained by Uma and at the beginning