<human>: My ex-girlfriend and I had a messy break-up. We broke up because of a whole complicated myriad of reasons, but at the end of it, I said some things that made her really resent me..

We broke up on the 23rd December, and she met a guy on New Years' Eve party. This guy actually dated one of my best friend's close friends so she has been relaying me all of the details. They've been going out since 2 weeks after they met and my best friend assures me he is a really sweet guy. My best friend tells me that she was quick to up the intimacy which only makes me think that this is a rebound. But hearing from my best friend, it really seems like she likes him. 

Meanwhile, this past month, I haven't been able to sleep or eat properly, losing 8+ kilos in the process. My emotions are really taking a toll on me and even when I tried to get myself out there, I couldn't look at another girl the same way I look at her. 

How is it that she was so ready to move on and so quickly too? Everything was fine until the end, there were no ongoing problems.

Summarize the given text in a few sentences.
<bot>: Girlfriend started dating again 2 weeks after we broke up while I am still dying inside, wondering how she got over me so quickly.