Nathan had succesfully blackmailed Joshua into allowing him to marry Millicent, and he figured the faster they married, the more quickly he could get his hands on her fortune, which is his only real desire in this union.
DARK SHADOWS never had good weddings that lasted for days and days, like other soaps.
SPOILER AHEAD!!!
Even when Carolyn Stoddard, the primary Collins child, got married, it was a quickie affair with very little preparation or fanfare.
And in the final storyline, 1841PT, there are weddings galore, nearly all off-camera elopements, with one very quick one in the Collinwood drawing room (Morgan and Catherine).
I guess Curtis didn't appreciate how much the ladies love weddings. Barnabas' wedding to Angelique was so fast, almost without thought, yet that woman haunted him based on those vows FOREVER!
Love, Robin