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I think you are missing the point of his action. He was trying to prove to his lover that he is not his father and his lover is not his father's new life. He wanted to show his lover that he would never abandon his son, his son is the most important and that his lover was not the type to leave a crying child. He was basically killing 3 birds with one stone. prove to his lover how their situation differs from his father's. get his son to eat something he did not like and also test his lover- I am pretty sure every good parent would want to make sure the person in their life would care for their child.
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Hi marry. Yeah, I was thinking about all those different things, too, and especially about the point someone made earlier that Maki is a single father. That kinda puts a whole new period on the imperative, doesn't it? I don't know, the testing part just seemed like such an act of Kabuki, and then I think about what it's like to be a parent, and yes, testing is good. All these things would've been revealed through the consistent passage of their relationship, but at the same time, it's a manga. There are only, what? 40 pages to get this message across before the next chapter? So, yeah, I forgive that father. Or, rather, I vacillate between "That was so paternalistic" and "Well, yeah, he's a father, so..." ¯_(ツ)_/¯
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And I considered that, too. He claims it was a test, so .... but you're right, it could be as much a demonstration of self-responsibility to his prospective lover as it is a show of power. It never pays to be overly indulgent with children, but if you're too strict and controlling, they rebel.
The problem with "Sneak Tests" is that once your date and potential partner are aware they are being tested, they are thrown off their natural stride. They fear showing anything but their best bib and tucker, as the saying goes, which defaults to counter-intuitive and ego-driven displays which focus on "becoming" rather than "being". So it's an unnatural and uncomfortable state of being which has the result of being like a mask or veneer of good behaviour which slips once they have achieved their goal, whatever that might be ... partnership, commitment, etc., because it's a goal-oriented process, not a "let's enjoy the journey" state of being. Once they have what they want, they go back to their default personality setting, which is who they were all along and tends to be considerably less shiny. Do you want to feel wary of your date or lover?
Welp, Mr. Dad, you aren't exactly cutting a fine figure of a man right now. I can understand the frustration with fussy eating, but is this really the hill you want to die on? Especially to trigger all those separation anxiety and abandonment issues your gorgeous lover already explained to you so carefully. Get him to show you his vulnerability and then reinforce it, is that the plan?
Why don't you just give your kid the right to turn up his nose at only two food items in the entire world as long as he eats everything else he's offered, and leave it at that? It isn't like there aren't other vegetables, and the limited right to choose will probably make your life easier. It will certainly be kinder to your lover.