It didn't seem to escape Nicholai's memory. Even if he was not willing, he had to bait Rowan Baldwin and Audrey Gillard with his own wedding. They even had to deal with a fight that broke out; they almost lost Dylan and Vivienne to those shadow wolves, too. He had sealed his mating ritual with Darius that night indeed… but what kind of wedding did they have?
Even Guinn wouldn't have that. All her children were wedded properly to their mates. There was no way she would leave Nicholai and Darius to some strange memory. This was why they decided to invite Darius and Nicholai tonight. Since they figured the two wouldn't come to their castle twice, they had to fuse the two events together.
Darius needed both the moon power and a memorable wedding.