Why do some women stay in abusive relationships?

A lady was badly beaten last night by her boyfriend. Not the first he will do so...but this time she decided to share what happened to her with a group on BB. She posted a photo of herself in the hospital, and later photos of her battered face. I have all the photos but the lady doesn't want the exposure so I will leave the photos out and just share the first message she put up in the group...

Thanks Everyone... Pls give me sometime I'll get back to u.. I put up d pictures bcos enuff is enuff of all this abuse.. They say they love u but still put u through this. I neally lost my life this morning.. My front tooth fell off and I can't walk.. It took me getting unconscious for him to stop hitting me, before I passed out I begged to be taken to d hospital, I told him I felt like I was loosing my life will he was beating me, that's the last I remember.. I woke up in d hospital

I wish I could share the photos. Incredible sad! A few hours later she put up a text message he sent to her begging for forgiveness..after which people in the group started advising her not to go back to him.

Go back? Should that even be something to debate about? Should we be talking about her going back to him or talking about how to get him arrested for attempted murder?

Why do some women stay in abusive relationships? Why do they go back?