The plot twist is indeed unexpected and bizzare but to be honest, me being a very keen observer found two very uncomfortable plot holes.
*** Spoiler alert***
First. I felt half of the problems were actually caused by the character Emma Beesly! How is that possible that someone imagines so much that they can't distinguish between reality and fantasy??? She literally imagined him to be physically present with her (also the makers of the show misguided the audience by repeatedly showing those scenes between Emma and Nick!) The stupid part was that the photoshopped beach selfie obviously never happened, then how was Emma even okay with the photo?? Or did she fantasise even that photo being real?
Second. Nick did have an account (prolly long ago) and spoke to Mandy for sometime untill he stoppped replying but he definitely had the app and recieved notifications which means when Dawn replied to Mandy as Nick, he should have received those notifications in his phone!!
Despite these little errors, the show is well made and definitely a must watch❤️