Cynthia,
You will find much of interest -- and much that confirms some of your theories about widows in the census -- in this article:
Samuel H. Preston, Siet Lim, S. Philip Morgan, "African-American Marriage in 1910: Beneath the Surface of Census Data," Demography, Volume 19, Issue 1 (Feb., 1992), pages 1-15.

The easiest way to access this article is to visit a local academic library that subscribes to JSTOR, an online repository of academic journals, and print a copy at one of their public computers.

If you do not have academic library anywhere near you, email me and I'll see if I can send you a copy.