Your brother is a petulant little asshole who, if he continues to act this way when out in the real world, will likely get his ass beat.
That said, you need to be smarter with how you engage in activity you wish to remain secret. Use the TOR web browser. Erase cookies and web history after every session. Create strong passwords that are unique for every site you regularly visit (a password manager like KeePass can both generate and store them for you). If you've saved any porn on your computer, password protect it, too.
Don't make it easy for them to find things you don't wish to see.
That said, you need to be smarter with how you engage in activity you wish to remain secret. Use the TOR web browser. Erase cookies and web history after every session. Create strong passwords that are unique for every site you regularly visit (a password manager like KeePass can both generate and store them for you). If you've saved any porn on your computer, password protect it, too.
Don't make it easy for them to find things you don't wish to see.
"I was thirsty for everything, but blood wasn't my style" - Live, "Voodoo Lady"