Honestly. I see nothing wrong with dating this woman and I see nothing wrong with rubbing your new relationship in your ex's face.

If I ever become lucky enough to attract a woman that's very physically attractive, I will show her off to everybody who has ever rejected or abandoned me when I needed somebody. I will make every girl that's ever dumped me rue the day that they did.

Retribution can be euphoric sometimes. As long as you aren't getting back at everybody that wrongs you, I don't see anything wrong with a bit of vindictiveness; if anything, it can be a good coping skill if used right and in moderation.