So my Ex and I broke up a while ago due to her cheating on me throughout the entire relationship. I devoted a huge portion of my life and money to her. We were even engaged to be married. It was a messy breakup. I ended up banging her sister after we broke up, who recently spilled the beans and resulted in a big drama for their family. 
While we were in a relationship, my Ex was claiming single welfare payments. I had a decent income at the time so she definitely wasn't eligible. 
WIBTA if I dobbed her into the welfare department (Centrelink)? They take fraud very seriously. It would result in them pursuing her for the money she claimed and would likely cause huge financial hardship for her. 
??? 