What's up with my ex?

My ex broke up with me at the end of July. We'd been dating for 4 months. She said the usual stuff: "it's not you its me", "I feel that I should be single for longer" "can we still be friends" etc etc haha. I agreed to remain friends and we broke up pleasantly and have been talking pleasantly via text since (which I had major doubts about doing) but recently she told me that she's already gone and gotten herself another boyfriend - someone who she's known for a little over a month. They've been together for about a week now. Is this a rebound thing?
What's up with my ex?
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