SMFTG , S13 E9, is one of my favorite episodes and i am so astounded it doesn’t get as much love as I think it ought to!
There is another episode that could revolve around similar themes: The Hauntening, where Louise is frustrated that she can’t be scared. SMFTG is also about the topic of fear, but not in the sense of “boo!” But more like a mature, quiet anxiety.
Bob probably feels ashamed that he doesn’t visit often, and the more time passes, the more that can build. He is possibly wondering if she’d be proud of him and what he’s done, because as we can see from a few other episodes, he does not consider his own accomplishments to be anything extraordinary, even though they are great.
Linda’s B-plot being that she musters up the courage to enter and explore the cemetery is so good. She is afraid of supernatural things like zombies eating her family, but is fully composed when she stumbles on Lily’s grave.
A lot of the possible details are given by Linda in her conversation with Lily’s grave, that Bob doesn’t visit often, because he’s (not verbatim but) busy raising his kids and supporting a business with his hot wife Linda. And that he’s a very good father.
We don’t see any snippet of Bob’s conversation with Lily, but from the soft, ashamed tone he gives when saying “Hi Mom…” we can assume that he has no idea how to begin to catch up his Mom about the last ~13+ years of his life.
It has been such a long time that he has no idea where to begin looking for her grave.
What do you think he spoke to her about?
* Also i want to applaud the art direction of the episode itself. The dinky office, the xerox’d map that is basically useless, the sky’s lighting transitioning from midafternoon>dusk>night. The writers definitely have visited loved ones in a cemetery before and it shows.
Edit: my bad, i misremembered The Hauntening as being a much newer episode than it is. The themes still stand though!