Welcome to the human race. Working on your self acceptance will support you in the grief process. I hope that, as you read this, you are not thinking that I am trying to talk you out of your guilt. Not at all. In order to get that 100 pounds of punishment, you have to feel the guilt, not avoid it.
Experienced grievers suggest a number of ways to help with guilt.
If you don't usually exercise, take a guilt walk. Turn your pain into art by writing about it, painting it, or building something you dedicate to the deceased sibling. Forgive others and ask forgiveness from God for yourself. Consciously atone for whatever sin you feel you have committed by doing some related volunteer work. The key to working through guilt is to make it conscious.