Pretty sure Tooru was already falling for Yuki around when she started to learn how to bake stuff. He forced those burnt things down out of love. They just spend way too much time together. Sakura never had a chance.
Yuki just keeps thinking she doesn’t deserve happiness. Those kinds of characters really get to me.
Nisekoi’s Chitoge got me falling hard for her for similar reasons. She was real possessive when it came to Marika’s overbearing advances that made Raku more uncomfortable than fond, but the moment her best friend was revealed to have feelings for him, she had a crisis of conviction, and then finding out he had feelings for said friend and running away before finding out he liked both of them… it was no surprise she did what she thought was right to leave them alone and run away, only for the obvious to happen and everybody worked to try and find her and bring her back. And he ended up choosing her in the end, and the best friend was strong enough to be happy for them and stay good friends to both. Really liked that story and it’s ending. Real tear-jerker, though.
It was kind of a similarly situation, too, in that the guy spent way more time with the one girl than the other, so of course he was more fond of that one.