I’ve mentioned before how one thing I appreciate about the show is the exploration of the many and complex reasons Natsume keeps how he can see youkai a secret from his foster parents. Usually this kind of thing is brushed under the rug or not explained all that much because it’s just a device to keep adults/civilians out of the picture, but with Natsume, his secrecy is part of his character arc.
He does trust the Fujiwaras. He does know rationally they’d still accept, believe and love him. But he also doesn’t want to make them feel bad. He doesn’t want to tell them the full extent of what he deals with because he doesn’t want to worry them or sadden them. He’s aware it’s for himself more than them- they would probably appreciate knowing the truth, no matter how sad it made them. But he just can’t stand being the one to tell them and make them feel sad.
The interesting thing is, the Fujiwaras do know that he’s suffered before now, as their previous conversation demonstrated. They don’t know the details, but they know he’s been through a lot of horrible stuff just by how he acts. They’re ALREADY probably sad about him to an extent and he just doesn’t realize it.
On the other hand, I do think he’s right and it would freak them out a lot to know youkai are trying to kill him every week, that he’s almost been killed a whole bunch of times. He is in mortal danger A LOT and it would be scary for them to know the full extent of that. Especially since there’s absolutely nothing they can do to protect him. They can’t see the youkai, much less keep him safe from them.
Ultimately, even with all that, I think they’d want to know the truth, even if it was hard. But I can understand why Natsume’s unwilling to deal with that. I think someday they will know the full deal with him, that Natsume will tell them. But it’s going to take a lot of time and growth on Natsume’s part to get to the point where he’s comfortable with that.