I'm very sorry to hear of your loss. I too had such a loss when my wife was killed by her mentally ill brother in 1992. It destroyed my family and hopes for the future. They say when you lose a child you lose the future, when you lose a spouse, the present and when you lose a parent you lose the past.
[As I'm writing this I'm having telrrible back and side pain but I'm trying to work and having a difficult time today...so please excuse my writing]. What I found that worked for me and how I've healed in the last 12 years is the following.
1) Seek a grief group right away and share your loss and feelings. It really helped me to take long walks in the desert and scream at the top of my lungs almost daily when needed. As a male, we often bottle emotions and it helped me to schedule these screaming sessions on my long walks.
2) Be sure you kow your boundaries and share with those you trust who can help. Mine made it to newspapers where I lived so everyone knew about it at work and even my neighbors. I often felt awfull bringing it up, but it did help to talk to friends. Some became distant and I lost their friendship, some trully cared and were true friends. Others didn't really care. I found by helping others I also helped myself. Eventually I moved to get away from all the memories to a certain extent. Good and Bad ones.
3) You will go thru many stages in grief: Anger, Resentment, Enlightenment, and even forgiveness if you chose to. I forgave her brother by writing him a letter while he was in prison. I get yearly updates and still dread reading his latest psychiactric charts every year, because it makes me relive to a certain extent my trauma over the whole thing. My wife's mom and dad have all passed on now and her only relatives are quite emotionally distant, so I grieve alone now after more than a decade. To each his own ..even in grief I've found. Do what works best for you. Fond memories of my wife always made me feel better and I cherish them still.
4) Exercise to help yourself feel better if you need to. Listen to lots of music that makes you feel happy and uplifted.
5) Read lots of grief books, they helped me see my way through tough times when friends and family weren't there 100%.
6) This is now a part of your life story, family history and legacy to your beloved brother. It helped me to be conscious of this fact in how I remembered my wife, always trying to keep a balanced view on the whole incident. For instance, I've since remarried and now have two wonderfull children. So looking at them and the love in their eyes I see how God has a plan for each of us and we really don't know why things happen like they do.
Oh we really think we do, but we really don't I've found. Everything, good and bad in this life is there for a reason. My favorite song to remind me of this fact is by Alison Krauss : "There is a Reason"