Is it dumb for me to be jealous?

I have a 5 year old neice that I don't get to see very often. She's at our house right now for the first time in 8 months and I'm bumbed that she doesn't really want to spend time with me. She told me that she wanted to go camping so I suggested that we camp in the house tonight so we started to build a tent out of a table and chairs. My dad starting treating me like I was an idiot and so did my little sister. So I abandoned the idea and instead blew up her air matress. Then I started to make it so that we could sleep down in the living room and she said that she didn't want me to sleep down there, she wanted Lisa (my little sister). Whenever I do something that makes her angry Lisa runs in to save her and makes me seem like a jerk. Ari always seems to want to be with her and spends all day hanging on her and telling her she loves her. Is it dumb that I'm jealous of my little sister and her bond with my neice?