Cheating in friend group

My friends both dealt with their cheating boyfriends differently.

D (27) noticed him locking himself in the bathroom for a very long time with his phone and other red flags. The second she could she got on his phone and confirmed it, she also reached out to the girl and asked for receipts.

Other friend S (25) was driving to Ross with her boyfriend, they were talking about a song and when she reached for his phone to put it on YouTube he snached it. He had never done this in almost 2 years so she new something was off. She stayed quiet and when they got to the store she said "You're hiding something so it's over".

As she walked he walked after her calling her crazy, paranoid, "Let me go get my phone from my car and you can see", she just called herself an Uber and blocked him on everything.

Our friend D asked S if she wanted to do some snooping and figure out what happened. S said she didn't need to know anything, she was simply done.

S has been dating for the last month and hasn't given her ex any access even though he hasn't stopped trying to see and reach her.

Yesterday we found out D went FBI on us and said she had some "receipts" on him. He wants S back so D got him to fess up as a last resort to get her back. S said she's not interested, she's over it now and doesn't care.

D says she needs to know since it involves one of our other close friends but S told her to "PLEASE STOP!! I already told you I don't give a fuck, I'm really happy and I don't care".

D got upset and said S needs to know since this might change the dynamic of our friend group.

I'm honestly on S's side, she doesn't seem to be on denial, she's very clearly just moved on and is happily dating. I just keep getting messages from D telling me "she needs to know". This is causing tension in our friend group and I'm not sure what to do. S is just a person of her word and knew something was off and trusted her gut, she also said she doesn't need "evidence" she trusts her instincts and that's it. How would you handle this situation?