I'm starting to think Miku might have breasts cancer if she grew so rapidly, but that's obviously fan service since most comments were "zomg boobies!!!!11oneoneone".
He was the first man a part from family who gave her attention, it's reasonable she "fell in love" due to low self esteem Miku has but that doesn't mean it would be "love" if you understand how it works.
Men have similar world view, if any girl/woman gives attention we see it as "is she hitting on me?".
That said, she doesn't really know what "love" is if Miku thinks it's "giving attention", it's just wrong, especially if good teacher is one who supports and gives attention.
Knew a person like that, low self esteem, craved attention but thought it's love if anyone noticed her, it was irritating and exhausting, not worth to drag any longer.