Mom remarries bff's Dad?

I'm a teen whose parents got divorced not too long ago. I honestly didn't mind if they divorced, as long as they were happy.
I think my mom has a secret relationship. But now, my sister told me it might be with my bff's dad.

I had seen was that once my mom comes into the kitchen and left her phone in the counter unlocked. She had sent a nude to someone. I didn't see the name of the contact (important, this is in messenger) What my sister told me was that once she saw mom texting someone in messenger, that someone was my bff's dad. And it would be normal because they are coworkers, but they called each other baby. My sister checked her phone since this is odd. And she scrolled through some pictures and found a different nude picture in there. She also saw that the Messenger app was locked. There was only a very specific way to get in that we didn't know. It's weird that she's being extra cautious with only that app. And before she let us use her phone and do whatever with it, now she's being more cautious.
I'm anxious. The idea of remarriage on its own is already weird. I don't want to be selfish but that's a big change. One I don't think I'm ready for. And now with my bff's dad it'd be worse because unlike me, she reacted negatively to her parents' divorce. (She's okay with the divorce now, and her parents divorced not that much time after mine did.).
We're not sure yet. But there is a lot pointing to it. I don't want my relationship with my best friend to be ruined if my mom actually marries that man. I don't want it to be awkward, despite the pretty good bond we already share with that family. I have such a good bond with her family. I don't want it to break. And I don't know if she suspects about it too, it's not like I can ask her. I don't want us to get bored of each other for being around each other for too long. I don't want things to change. I know it's selfish. But I can't help it. If it does happen, what should I do?

Mom remarries bff's Dad?
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