Hi Catherine,
can't help with the census but this might be the marriage of John Senior. Note it's by licence, so more information there if you track down the Allegation.
from the Sussex Marriage Index:
Whatlington, East Sussex, Date: 22 Oct 1794:
John SIMES
Hannah HUNT, (lic)
This looks highly likely as the marriage of John junior,
from the Sussex Marriage Index:
Hastings St. Clement, East Sussex, Date: 28 May 1840:
John SIMES, Sedlescombe
Caroline CROUCH
Jane