I feel like I want to delve into a thousand different thoughts I have reading this, but this is too heart-wrenching. Mentioning the instruments made me think of times when my spirit was so low, I didn't even want to play the piano or sing, because it's like that part of you that is empty. Those two lines about the organ and guitar made me feel like this goes even deeper, that your spirit is broken and these little things that would bring you joy, give you purpose, they're not present. Literal pieces of you can't properly function anymore.
That question of "Do you?" is a like a plea to understand why you are grieving, or perhaps with you being happiest there gives you the chance to ask and wonder and feel. I read others' thoughts too but the way I took it is that you feel better at the grave. More complete. Because living a life without them, not going to their grave and visiting them would be letting life continue and accepting there's this opportunity to move on. That's how I could see it at least but like Jamie said, there are so many different paths this could take. But it's personal to you and I just feel a field of grief in this.