I have a sudden realization that my little brother has destroyed my life
What makes you think he destroyed your life?
It feels like he has taken my entire existence
Dont allow your sibling to ruin your life. If you feel that your sibling is taking away from your life then do your best to get him to be more independent. If this is not possible then think of some ways to treat yourself as well so you can be happy.
The only thing that will fix this is if he spends more time with me and less with my friends, or I will kill him.
I can understand being upset with your siblings, but you need to work things out instead of letting this destroy your life. You will have a better time if you can spend time with your brother and your friends.