It's also been noted countless times that Adalind basically went through a similar situation with her powers returning but why did N/A succeed where N/J failed? I think at the time of Juliette’s confession she had already given up on her relationship with Nick so when he doesn't respond the way she wants, it's like a confirmation of what she'd long decided, to end things between them. It was impossible for Nick to respond with nothing but acceptance of something so shocking and unexpected happening to Juliette. He made several mistakes yes but nothing that couldn't be worked out given time.
With Adalind, he'd been living with the knowledge that someday her Hex would return although I think he was hoping it would be in the distant future. When he found out, he was mad that she had lied to him but he had a cooling off period because of Rosalee talking sense to him to wait and see, something Juliette never had. She'd turned to the wrong person first, Sean Renard. Henrietta was a good idea but the mistrust was building already. Just like before, Nick didn't want to lose what he had but unlike before, Adalind wanted the same thing and was willing to work towards keeping it even with the hexenbiest back in full force. Juliette didn't.
With Adalind, he'd been living with the knowledge that someday her Hex would return although I think he was hoping it would be in the distant future. When he found out, he was mad that she had lied to him but he had a cooling off period because of Rosalee talking sense to him to wait and see, something Juliette never had. She'd turned to the wrong person first, Sean Renard. Henrietta was a good idea but the mistrust was building already. Just like before, Nick didn't want to lose what he had but unlike before, Adalind wanted the same thing and was willing to work towards keeping it even with the hexenbiest back in full force. Juliette didn't.