It sounds like you and your Grandpa were very close. It is always difficult to lose a loved one. You may try thinking about how he would feel if knew how upset you have been. Would it make him feel bad if he knew his death was doing this to you and there is no way for him to help you like he used to? Think of what he would want you to do to ease your grief for him. Maybe he would want you to just be grateful for the time you had together, feel blessed because not everyone is lucky enough to have had a loving grandparent or ever had a chance to even meet them.
I don't think he would like that you are upset with life because he is no longer here...I think he would want you to remember him with joy and celebrate his life by being the great person he knew you would be. Make his spirit happy by enjoying the life that you have left to live. Time heals all wounds, and it will happen for you, too! Best Wishes.