damn man. Terribly sorry for your loss breh.
My uncle was murdered last summer and the killer is still alive and roaming on this earth. It took me 3 full days to get everything out of my system but once i did, i was ok. I still have flashbacks to that day and i get angry but i take solace from the fact that, god willing, he is in a much better place.
So to you breh, i'd say, get everything out of your system. If you gotta cry, cry bro. Go to friends, family, whomever and let it all out. If you keep stuff bottled in, it won't be good for you or your health.
I know your mom ain't comin back to you and the fact that you weren't there to do anything really hurts, but she is in a much better place breh. With her creator.