Read this BBC article, Highlander's sex slave past unearthed, to learn about the abuse of slave women on plantations in the West Indies. Letters documenting the abuse will be part of an exhibit co-curated by Dr. Karly Kehoe of the Centre for History in Dornoch.
While reading descriptions of such goings on is undoubtedly unsettling, I don't think such relationships between slave owners and female slaves should be all that surprising. These sorts of goings on were quite common in the American South. An anecdote that I heard somewhere (can't remember where or when) is that a plantation owner's wife could name the fathers of all the mulato children on all the plantations around, except on her own.
With thanks to SKKehoe.