'Hadn't Henry fallen in love with her when he and his father travelled to (Dover?) welcome and greet her to the country...............?
Then a while later (was it just months) when the brother died, Henry married her.'
No. He would have been about 10 at that time. She was older than Henry by about 5 years.
Yes, she was married to his elder brother, Arthur, first. Arthur was always weak and sickly and died months after their wedding.
Catherine, who was very religious, swore many many times on her immortal soul, the Bible, what have you that the marriage was never consummated.
Once Arthur died, however, Henry VII was quite hesitant to send her back to her father, however, because it meant he'd also have to give back the bulk of her dowry.
So that's where the plan came about to marry her to Henry.
It required special papal dispensation, because the Bible forbade marrying one's brother's wife, but that was arranged because the Pope was related to the Spanish royal family.