Right away the great mystery behind Nan-gil's motivation is fully cleared up- and it ends up being really, really corny. Weirder than that it's actually kind of oddly consistent. Considering how outspoken Nan-gil has been around Na-ri it initially seems completely inconsistent that he's maintained a comical and borderline creepy lifelong obsession with Na-ri. Yet it does make sense because of course Nan-gil has never seen Na-ri as a person but as a metaphorical representation of the family Nan-gil could have if he's a good little boy.
Meanwhile Na-ri and Deok-bong don't have a clue what's going on in Nan-gil's head, and that only makes their preposterous hypothesizing all the funnier. It's also amusing how Na-ri and Deok-bong actually have a lot in common personality-wise, and this is what makes them not really work as a couple at all. They encourage behavior in each other that, while not exactly bad, is clearly not ideal and is not at all condusive to emotional growth.
While Deok-bong's generally crummy attitude was fairly obvious last episode, Na-ri's similarities are becoming more obvious the more background information we get. Nan-gil swooped in and improbably saved the day precisely because Na-ri was not paying close enough attention to her mother or the greater family situation to do so herself. And even now Na-ri is far more obsessed with Deok-bong's obvious eccentricities than those of the other characters she runs into.
Where this leaves us is Na-ri finally making an essential revelation about this situation that doesn't go into silly daydream fantasies and...well, I don't want to ruin it, but the final scene is genuinely sweet. It's nice to see that even without knowing the absolute full story, Na-ri can still recognize genuine emotions in other people. That's an important step up from her falling further to Deok-bong's generally cynical level.
Another fun irony is how the generally absurd situation with Nan-gil is a fairly effective distraction from the far more traditionally annoying plot involving Na-ri's ex-boyfriend and traitorous co-worker. Those two are just silly as always. Yeo-joo seems to want attention more than she does anything emotionally useful. And Dong-jin isn't much better. His half-hearted measures to get back to Na-ri are completely uninspiring, and those too serve as a useful argument for why Nan-gil's sincerity matters so much. Nan-gil is pretty much the only character in "The Man In My House" who actually wants something, however silly that goal may be.
Source:HanCinema
