Robbie,
I bet she really did fancy you - very much!!
But, like you said...she's an abused woman with little self esteem. It is unlikely that she has much confidence in any of her choices. She's probably getting back with her abuser because he sold her a song and dance about how he's changed, how great things will be now, it's better for their child, he'll never hurt her again, he's got a great place to live now, etc.,. and she thinks she 'owes' it to him and their child to try once again.
But the only thing that is going to happen for her is that she'll eventually be abused again, by that man.
She didn't get involved with you to 'make him jealous' or to 'make herself feel better'... She just can't think for herself.
When your friends tell you to run a mile from a *bad date*, next time you RUN!
Chalk it up as a learning experience and don't date anyone like her again.
Best of luck to you! Hang in there.