Andy,
I am so sorry for the loss of your brother. Not only are you mourning the loss of your brother but you must also be mourning your own personal loss of your kidney. When we become donors, and I think especially sibling donors, we form a physical bond in addition to the emotional bond of being siblings and sharing family history. We all have hopes that our kidney will be the one to save our loved one but we all know there are no guarantees. I hope you can be comforted in knowing that you did such a wonderful act of kindness for your brother and I'm sure he appreciated you even more for it.
There have been other donors on this forum who have experienced a similar loss. You can try and do a search to see if some of those threads pop up.You can even contact the transplant center and see if they have professionals who would be willing to talk to the donor of a recipient who has passed. Maybe even the NKF can offer some emotional support as well.
May the memories you have of him be a source of comfort to you.
All the best,
Sherri