How many times did Brahmo Samaj split?

After a decade of decline, it was revived by Debendranath Tagore in 1843. A schism divided the organization in 1865, when Keshub Chunder Sen split with Tagore and formed the Adi Brahmo Samaj, and in 1878 Sen’s group itself divided into certain splinter groups.

For further reading check the following articles:

• Raja Ram Mohan Roy
• Bengal Sati Regulation
• Indian Education System During British Rule