Natalie :catbite: (@Natuwu)

I could fill back in that grave
I could hammer in that nail

As he's feeling a bunch of different emotions, he has different impulses on what to do. He could move on from it and try not to think about it. The grave comes up repeatedly in the album as reference to the painful emotions of relationships and breakups. In filling in the grave and nailing the coffin he's saying he could try to block it out, living a life of not feeling anything (hammering in the nail). But he's unsure if he wants that.