They're what I call attention vampire. All they want from u is ur attention. If u give them, they feel satisfied and will put u aside. So the only way to deal with them is to not give them the attention they seek, and show that no matter what they do, they can't affect u at all.
Attention, wanting to make you jealous... the possibilities are endless but try to not just assume it's about you. You might interpret it as her "parading a new love interest" while she could really just be living her life with hew new partner.