Baggins is a two-year-old domestic short hair. I found him in the forestry near my house when he was only weeks old. He was starved and very nervous. It took a long time to build trust between us as he was terrified of everything. After months of building this trusts, he evolved into a very energetic, playful, and curious kitten and continued like this as he began to mature.
However, in the past 4 or 5 months, he has become skittish and nervous all of a sudden. He still trusts me and spends hours sitting in his nest on my desk. However, when he hears or sees my brother he freaks and bolts. My brother doesn't spend as much time with Baggins, but he isn't cruel and I don't think he would ever hurt him. I'm very confused and was wondering if anyone would have any answers or solutions to this problem. It's come to the stage that when I open the door for him to come inside, he looks and listens before entering in case my brother is home. I feel terrible seeing him like this as he conveys visible terror and I don't want him to be scared in his own home. I have read animal psychology books and tried finding answers online but at this point, nothing seems to work. Thanks for your help! :)