Have you done any research in other records besides Census? There are lots of additional records to look through to find your answers, including one of the most important, Marriage Records; don't limit yourself to Ancestry.com, they have lots of records, but not everything, however, they do have death certificates thru 1975 (NC only started using d/c's in 1913, so you won't find anyone dying prior to that), so if you have a subscription to them, make sure you use their searches.
FamilySearch has a great collection of North Carolina Records, including Marriages 1759-1979, and this is what I found:
Name: Jacob Smith
Birth Date: 1823
Spouse's Name: Agnes Bishop
Spouse's Birth Date: 1833
Spouse's Age: 40
Event Date: 15 Jun 1873
Event Place: Halifax, North Carolina
Indexing Project (Batch) Number: M75256-0
System Origin: North Carolina-EASy
GS Film number: 317209
Reference ID: page 6
Looking at the Census, the couple were lying about their ages, but hey, that was their business.
If you've never used FamilySearch before, try it:https://www.familysearch.org/
Put in a name, Country (United States), click either the link for "Marriage" or "Residence", and fill in Halifax, North Carolina (the word "county" not needed), then click SEARCH. You can further filter results that come up by clicking the "Collection" option on the side, and choosing any of the collections broken down into Birth, Marriage, Deaths; Census, Military, Probate, and whatever else. Lots and lots of great records here.
One of the things I can tell you about the 1870 Halifax Co. Census is that it is totally messed up, anyway, because the census takers screwed up with the numbering, as well as apparently having several different people taking the census for the same neighborhoods in some cases, lots of numbers are crossed off; some families are counted 3 times, while others have members scattered over several different pages. You might notice, for instance, some households where there are nothing but very young children, but careful studying of the family, will show that they actually belong to a family sometimes as many as 10 pages away. I have no idea what they were doing that year, maybe the Census takers were still in shock that their population had tripled and that they had to count former slaves or something.
In the Halifax County Cohabitation Marriage records of slaves, from the book "Somebody Knows My Name, Marriages of Freed People of North Carolina", by Barnetta M. White:
JACOB SMITH was married to LOUISA _____ in 1854: obviously his 1st wife, so AGNES was his 2nd wife, which is why they weren't together in 1870.