Tomorrow makes it a month

I lost my baby brother last month unexpectedly. I still can't believe he is gone. We grew up together and lived together for over 20 years. He complained of a headache, went to the hospital by himself and I was notified the next morning that he passed. I've never lost someone so close and I didn't know how to process this pain. I've been on autopilot ever since. How do I deal with this?