I'm sorry...
We all lose people in our lives. A little over 6 years ago I lost my dad to cancer and my two cousins in a car accident. Sadly, we can't change the past. I can't imagine how hard it must have been for you to write this. You've reduced me to tears, and crying is something I don't do often.
Why do these things happen? Who knows... Just remember, you're not alone, there are many others who feel the same way you do.