Feeling guilty over a gift from someone I grew up seeing as a brother

As-salamu alaykum. My family setup is a bit unconventional – I was taken in as a baby, not through formal adoption, but raised among them. My older siblings are all related to each other, but I’m actually their cousin, even though we were brought up like real brothers and sisters. So the brother I’m talking about here isn’t my mahram, but my family doesn’t see it that way, and I don’t want to cause any hurt, especially to him. He’s always been just like a big brother. I started wearing hijab a few months ago, but sometimes it’s hard to keep it on around him. I end up covering with a hoodie and a hair bonnet instead. Same with the man who raised me. It hurts because I feel like I’m being cold towards my brother when I’m used to joking around with him. He’s much older than me, so it’s even more awkward. I care about him deeply – he is my brother in my heart, even if not by blood. But now I feel forced to act distant. Today he gave me some stickers because he knows I love them, and I put one on my water bottle. Immediately after, guilt hit me. I started thinking – is this sinful? Should I peel it off? I’m only here for a short visit before I head back to my studies, inshaAllah. The guilt over something so small is eating me up, and I don’t know if I’m just overthinking or if it’s really wrong.