Many if not most JW's who were raised in the "truth" have no idea what love is because of the mechanical character of relationships in the JW family and at the KH. As a result, after they leave many get involved in abusive relationships that lack mature love based on respect because it doesn't feel foreign to them.
You are likely co-dependent, which is described as sacrificing (a very large portion) of your quality of life for that of another. Leading up to this event, you likely saw many things this girl displayed that were troublesome, but ignored it....just as you were trained to do to try and preserve relationships in the cult.
You should seek help yourself and learn to make choices based on truth, reality & goals and not feelings.
Sorry if this sounds "preachy". Its just my take.