I accidentally saw messages about me on my best friends phone?

so my “best friend” lives with me. She just bought a new phone and so her old phone is left at home but somehow still connected to her new phone. this morning her alarm was going off and she wasn’t here to turn it off, i went in to turn the alarm off and i saw a message from her boyfriend that said something about me. so i clicked on it to read the full message, and there were heaps and heaps of messages about me to him, ALL LIES!!! actual lies!! she was bagging me in every way possible to him. she doesn’t know i saw the messages but i feel really hurt about it. what would you do?
I accidentally saw messages about me on my best friends phone?
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