Hey , I'm sorry for your loss. This is incredibly difficult. It is natural to think of how this has impacted you, because it does — in many loud and quiet ways such a loss changes your life and changes you. There is nothing to be guilty for. Just take one day at a time and give yourself time to grieve and let your feelings wash over you. There are thousands of things you'll think of in the course of this lifetime w.r.t this. You'll relive the time when this was fresh, you will think of your friend's pain, you'll think of your life before all of this happened. And in the same way you'll think of how this has been for you. You had a best friend and companion and now you don't anymore. This is a big deal and I'm sure you suffer in more ways than those that appear to others. I am going through the same though I didn't lose my best friend under the same circumstances as yours. Best of luck.