She’s staying even though he cheated?

My best friend has been dating her boyfriend for a little under a year now. Recently a random girl brought up the fact that my friends boyfriend was recently asking her for nudes and flirting with her and saying how badly he missed her. Him and the random girl previously slept together, and the BF’s infidelity in his last relationship also had to do with him jumping between his ex and this other girl.

He apparently blocked the random girl now - after she confronted my best friend, but my friend is still sticking by him and posting like they’re okay and I’m having a hard time supporting her because of how badly I perceive his actions. How can he ruin one relationship and then practically a second with one girl!

I’ve kept my opinions mostly to myself, but her staying with him cannot be a good thing right?
She’s staying even though he cheated?
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