Honestly its possible you still have feelings for this person and you still care which is a positive because in life when things don’t work out its a good quality to have to know and accept that, move on but never stop caring. Its sounds like you can feel her negative energy and shes gaining from it. See when your in a relationship and feel good about it you don’t have to post it socially, brag, etc. Because everyone can feel and see the positive energy and love evolving from it. I also sense that their relationship is not genuine and they are not secure with their relationship. Its as if they are feeding off of showing off instead of each other. They like the attentions and the possibility of making ex lovers jealous. This is not a positive relationship.
Best thing you can do is steer clear and worry about your own because you have some amazing life events headed your way 😉
-Blessings!