As sad as it is how David ended up i guess its realistic
Going by how he acted in the original series, he was always kind of a couch potato and a weak artsy type of guy, it is hard to picture someone like that growing up and getting a full time job and raising a family. I guess it makes sense he grew up to be an absent dad traveling and doing charity work, nothing that really tied him down and put alot of responsibility on him.
Before this episode i actually thought he may be some kind of comic book artist, but i guess that would have been an unrealistic scenario. I like the way they did it, it made it feel more real, alot of the time a teenagers dreams of doing something doesn't come true and sometimes they do end up like David.