Hello charlieee, when you feel happy and guilty at the same time, it's because you already have "survivor's guilt". You feel bad that you're enjoying life while your grandfather's life is near the end. My oldest brother was 17 years old when he was murdered, and now that I'm more than double his age, I've experienced survivor's guilt every time I enjoyed something that my brother never got to experience such as graduating from high school, college, etc. Each time I partied or vacationed and experienced something beautiful, I would cry because my brother never got to experience these same life experiences. The difference between my brother and your grandfather is probably the fact that your grandfather has likely had a long and great life full of beautiful memories, and he will pass away from natural causes as opposed to someone taking his life. I'm sure that he wouldn't want anything more than for you to continue living your best life in his honor. Forget the past mistakes, leave nothing unsaid and leave nothing to forgive. Make the best of what's left. Tell your grandfather how much you love and adore him. Bring up your old favorite memories of him, and play his favorite songs. Take many pictures and video together that you can treasure later. Best wishes.