Just let her be IMO, when people get like that theres really nothing you can do that'll help the situation. Focus on yourself and move along, if she contacts you or anything then great, if not then its in the past. Sorry you had to go through that.

Leave her alone. Be civil if you run into her and have to interact, of course. I find that the only way some people can "get over" a relationship is to let anger win. Otherwise, they have to deal with the pain and let their love evolve rather than stamping it out with negative emotions.

I think it's a symptom of toxic monogamy taught by many popular religions and media and accepted in most societies that requires that a person "fall out of love" with a previous partner in order to prove their love for a new person. Personally, I believe most of us are capable of loving multiple people at the same time without diminishing the love for any, but that's not the most common way of thinking. So, most are taught by family, religion, and/or TV to turn to anger or even hate to mask the love they still feel for a previous partner.