My sister’s boyfriend is always horrifically nice to her… and I don’t know what to do about it

The first few times he did it I assumed it was a joke. He’s fucking with her, or with me. But he has been too consistent, and he’s been doing it too long.<br><br>He’s too nice, and I think he’s planning to hurt her. But what? He’s already been with her for almost a year now, and she’s fine. Better than fine, she’s happier than I’ve ever seen her. She laughs at his jokes, tells her friends about how good he treats her, doesn’t even argue with him. It’s not normal.<br><br>But I’ve seen it too: he’s always kissing her, always talking about how proud he is of her, always making sure she’s okay. He smiles at her, real big and wide, like he’s actually happy to see her. He says yes to her all the time, always does what she wants. It’s not normal. But she thinks it is. I think she even likes it. She doesn’t even see how weird it is.<br><br>I don’t know what he’s doing, but I know he’s planning something. I can tell. But I don’t know what it is, and I don’t know how to tell her. She’s so inside his little bubble. He’s been working on it for fucking months. Months. I’ve fucking seen it. Slowly but surely, he’s made it inside her head. <br><br>It’s not normal, and I know it’s not normal. But I don’t know what to do about it. I don’t know what he’s planning.<br><br>But I know this: if she says I’m the bad guy, then I’ll be the bad guy.