Satella did Subaru a favor of forbidding Subaru from telling anyone for people can take advantage of him if they know ( roswaal would just keep killing him) or put Subaru in bad positions thanks to their knowledge ( like al or imagine the cult/todd just imprisoning him keeping him from dying it would be hell )
I mean, sure. But think about how that’s gonna come across to people who see her as an individual and not a character — and ESPECIALLY as an individual whom they are not primed to give the benefit of the doubt:
Subaru somehow gets transported to another world out of nowhere, without any warning, and entirely against his will. The only real suspect that they have as to how that happened in the first place is the Witch of Envy.
Subaru can die and come back to life. Nobody ever, like, TOLD him this: it just happened. It’s painful and deeply traumatizing, and he’s given no explanation for how or why.
Subaru is forbidden from telling anyone about what he’s going through via the threat of bodily harm. If he tries to tell his loved ones anyway, then the Witch of Envy apparently has no qualms about killing THEM instead, and then leaving him to suffer the consequences. Puck straight up tortured him to death because he was left to take the blame for her killing Emilia, even.
At one point the Witch of Envy possesses Emilia and starts rampaging across the Sanctuary, explicitly because Subaru FINALLY managed to get someone to hear him cry about his trauma. She kills everyone he cares about and then attempts to trap him by her side forever, and the only way he gets out of it is by killing himself on the spot.
Subaru has a deep, instinctual affection for the Witch of Envy despite never having even heard of her before in his life. He was also attracted to Emilia specifically because she looked like the Witch of Envy (long, silver hair). He has no idea who this woman is and yet he’s apparently deeply in love with her. …In a world where magic exists, it is not at all a stretch to say that the others would grow suspicious that she straight up BRAINWASHED him into falling for her.
The Witch of Envy and Satella are two different people, but like. They’re still in the same BODY. And they both still have this very strange fixation on Subaru, who doesn’t remember meeting EITHER of them. —Hell, for all the others know, the Witches were straight up lying about them being different people after all.
Subaru wants to save her. He has absolutely no idea WHY he wants to save her.
Like, what conclusions would YOU draw from all that? Lol