The "sending videos" element to me is the most reasonable aspect you can criticize on this ending, here is why:
1. It hurts realism.
2. It is stupid on Zack's part, he really gains nothing from it, but has much to lose if Felix exposes those videos.
And the most important
3. It conflicts with the "alone and forgotten" theme of this ending. I think it would have been better if no one, not even Zack, gave a shit or thought about Felix anymore, amplifying the hopeless and despair.
The "video letter" thing to me it felt, it was there because it's a classic ntr trope rather than because it was integral to the narrative.