Though you may feel the need for revenge getting in the middle of their relationship probably would not work out the way you are hoping. More than likely she will think you're just being spiteful. I would let it go because if they are meant to be then they will be. Sometimes we don't realize that the end of a relationship is really a blessing and allows us to find the relationship that is really supposed to be. Relationships don't always work out but they always teach us something. So though your ex did not turn out the way you had hoped revenge would not solve anything. Just focus on yourself and let him be and good things will happen for you.