If your ex had rebound sex a week after?

So my girlfriend broke up with me a week ago, last night I had rebound sex. I feel horrible about it today, but I kinda enjoyed the attention that this girl showed me and the sex was great. I am now worried that since it's only been a week, that if she finds out I will have no chance of getting her back. OR I was told that it could be the opposite and make her really jealous (since she knows her) and she will want to take me back. Ladies, what is going to happen here?
If your ex had rebound sex a week after?
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