My Ex Is In A New Relationship But Keeps Sending Me Abusive Messages, And Tells Me How Happy She Is?

[Jeremy]

We were together a year, she was completely in love with me, but her paranoid and insecure behaviour started to suffocate me, this would push me away and she would get very angry that my behaviour started changing towards her, she would then do things to try and make me jealous to make me 'love her more', and this would push me away even further. I loved her very much but I eventually felt stressed being around her because of the pressure she put on me, eventually I couldn't take it anymore and I broke it off.

We saw each other a few times and she tried to win me back, the last time we saw each other we both agreed it was finally the end, and that if we saw other people we'd keep it under wraps.

A week later she texts me to say shes seeing someone else (rebound?) and ever since has been flaunting it as much as she can all over social media, I tried to win her back but it didn't work, after I'd given up she's been sending me abusive messages, telling me how amazing the new guy is, how she's in the happiest relationship she's ever been in, what a mistake I was, how she never loved me, how pathetic I am, how she hopes to bump into me so I can see how wonderfully he treats her, I'm a disgusting human being and I'm a c****, then tells me over and over how happy she is. She didn't flaunt our relationship over social media, she was single a year before I met her, and ever since I blocked her on facebook, theres been nothing, shes completely given up, she knew as soon as I'd blocked her and started sending abusive messages.

Now I know this might seem like very transparent behaviour but its nice to get some clarification because she's hurt me a lot with all of this, and I was looking on some advice on how best to deal with it.
I don't understand how she could meet someone a week after me, after saying she was the only person she ever wanted to be with, 2 weeks before, and be happy and in love, whats she trying to do?