Complex sentence: Townsend had nothing to fear from the men on his left because they were a company of his own regiment who had become separated from the main body but by the time this was discovered, Townsend had pulled back.
Split into simpler sentences: Townsend had nothing to fear from the men on his left because they were a company of his own regiment who had become separated from the main body. By the time this was discovered, Townsend had pulled back.