So sorry for your loss. My Dad was in his seventies and that was hard to watch, I can only image how difficult it has been watching your young bother’s life change so dramatically. The end is brutal.
All I can offer is that with time, the tears and bursts of grief do come less often, at least that has been true for me.
Remember the good times shared and perhaps focus on a to do list of things you think he would have loved to see or do with you. Speak his name often so those around you can experience what he meant to you and offer their support. Good luck.