@Maggienbub
Perhaps look at it as those old friends and your sibling as being in recess.
Some don't know how to deal and others may have shown that they are not cut for someone else's trauma and have moved on. Some friends are seasonal and some are lifers.
At the weekend just gone I had a catch up with two girls I went to Tech School with, one neither of us had seen for 44 years but what was obvious we all had a deep connection and it was like we picked up from where we left off from, that last day at school and 5 hours later we decided we'd better come up for air and we will do it again and the group will be a little bigger next time as we look up friends from long ago!
It's important at this time that you surround yourself with positive people and yes the one person I wish I could share this wretched journey with is my Mum, she died in 2008.
Take care