I’m worried my friend will find out?

A few months ago I slept with someone that my friend has slept with before. This doesn’t seem like a big thing but at the time I knew that she did quite like him so now I’m really worried that the truth will eventually come out. His best friend knows that we have slept together but he hasn’t told anyone or said anything yet. All it was was a one night stand and the girl isn’t that close with me at all but I know she’d be upset by it and mad. I don’t quite know what to do and now I’m over thinking and worrying that it will come out. Only way it would come out is if the best friend says something to someone that me and him are friends and he said he wouldn’t so hopefully he won’t but I’m not sure. Advice?
I’m worried my friend will find out?
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