In the first half of the second season, Nick and Sabrina broke up after Nick agreed to withhold the devil inside himself in order to protect the coven.
Sabrina was able to free him of the burden, but it continued to scar him and the trauma led to a breakup.
Nick was haunted by the ordeal every time he was with Sabrina, and it had put a huge strain on their relationship.
In the end, he left Sabrina and formed a relationship with Prudence (Tati Gabrielle), leaving fans heartbroken.
The second half of season two saw Sabrina and Nick somewhat rekindle their relationship, but it was not long-lasting.
source: express.co.uk