Do to an argument do to the way she is always talking to other guys even if she hasn't cheated still did it anyways and, was always quite the jerk at times you decided to break up with her after the argument but your sadly in the same school.

She may try to gloat a lot probably might be trying to move on and date someone else she'll always brag about how her life was better to hide what's underneath, even before she bragged and now was a bit more petty especially if it came to you.