the thing about victor frankenstein is that, aside from the deeply unpleasant but distressingly period-typical views about women and his polar exploration sunk-cost fallacy attitude, he's not even really an outstandingly bad individual. spending two years trying to make a whole person with no solid plan for what to then Do with this person is an extremely extremely bad idea, but after that all his reactions to stress and tragedy are fairly common and natural. avoidance, depression, decision paralysis, secret keeping, etc., these are very normal trauma responses. they are just literally all of the very worst responses he could possibly have had given his particular situation.
The “I thought that was non-diegetic” line has everyone thinking the Doctor can hear through the fourth wall, but what we’re actually hearing is his internal soundtrack he’s got going all the time. You better believe the Doctor wrote several full orchestra playlists he either sings to himself constantly or the tardis beams into his head nonstop.