Why am I so mean to my siblings yet I feel bad about it afterwards?

Being the only child for 8 years, it was tough and I wanted a sibling dearly. I'm now a big brother, in highschool with 2 brothers and 2 sisters. (The 2nd oldest being 9) My question is, why am I so mean to them? Even though I cherish them so much? I mean when I get mad I can't control my temper? An example is whenever I see my brother picking on my younger sibling, or brother doesn't share my iphone with my other siblings I would do things that'll make the one who's being "mean" regret it? I would say "Oh I'm changing the password for your game" and make them wait for like a few weeks before I give it back to them. I mean why can't I just stop them from fighting or make him have a time out or something? Why do I have to be so violent? Why can't I control it? The thing is… They don't even fight back, or hit me. They just cry and say "no" and then just go off. Seeing their reaction makes me feel bad, that why did do that and why can't I control my anger? I take it that my siblings probably think I'm the worst brother who always hits/boss them around, but I can't control it? I remember this one time when my brother had a essay in elementary about something and he writing "I Love my big brother" it was the best feeling ever… Even though I hit them, even though I'm bossy and mean to them he wrote an essay about me… And I still continue to be mean around them.

You are mean cause that's what older siblings usually do, you feel bad because they are family