I was just re-watching the OG producers walkthrough of Sims 2 and the scene where Sarah's sister see's Don kiss Dina and then proceeds to go and TELL Sarah what she saw then Sarah goes to confront him. Is there a MOD or anything to get that interaction? OR something similar? Even telling on a sibling for sneaking out or being mean to the other! I don't know why I'm so invested with the idea, but I'd LOVE to have this in a game for more Drama!

Not really a mod, but this can happen with the vanilla game, @melodycc_2004.
Don't take my word for it because I've never tested it in game, but I heard that Sims' partners can learn about cheating through gossip. So, potentially you could force it to happen if you spam the interaction soon after someone witnesses it.

Really? interesting I'll have to test that out.

No, that doesn't happen, sims don't know what the gossip they spread around actually is. My sims frequently tell their own spouses about their cheating memories and nobody reacts to any of it. Gossip is pretty much inert. A lot of these promo videos featured stuff that wasn't actually in the game.