Why would my ex go back to his ex who after their break up slit her wrists and stalked him?

My exboyfriend went back to his ex-girlfriend whith whom he supposedly says he tried to break it off with in their final 6 months. After he finally found the strength to do it, she slit her wrists and was sent to the hospital, finally after she left the hospital she woul went in front of his gate for hours at a time hoping he would come out, sent him emails and constantly called hi. Me and him broke up over a stupid misunderstanding due to text messages and now I have seen him back with his ex again.. How could or why would someone go back to their ex who had tried to commit suicide? What would there be to get out of it? And am I being stupid for wanting my ex back because I think the reason he broke up with me is stupid and he could do better being with a girl like me than his ex?