I notice a lot of people on here saying frequently that they don't understand why some women keep returning to violent or abusive relationships, and I read this book on the subject recently and found it really interesting, if hard going. It's written by Erin Pizzey, the founder of Women's Aid and is about women who are drawn to abusive (predominantly violent) relationships time and time again.
There are graphic descriptions of abuse in the book so just be warned if it is likely to upset you. If you think you can cope though it's well worth the read - it's quite short, 183 pages in print.
The book is called "Prone to Violence" and the whole text is available online here, (which is where I read it) or amazon link here.