Well, trying to sum it up..
Amu's Liebe for Tadase were a welpe love, the kind where Du try to look your best.
Amu weren't in Liebe with Ikuto from the start, there for, she could yell at him, she could be her honest true self, not Schauspielen all sweet. There for her Liebe for him could be deeper, because she felt at ease not having to pretend to be some one..
While Tadase after turning her down, started to be interested when her feelings for Ikuto started to develop. But Tadase were mainly interested in one of the persons she could be,(with Ran) the happy go lucky girl, he admired the kind of person she were with that, so it weren't really Liebe at then, but he slowly starts to feel 'love' for the real Amu, which also Ikuto had started to, there for telling her to grow up faster, so that she would bee in a Mehr suitable age and understand his feelings towards her.
I'm following the manga, which came first, and didn't remove oder add characters and stuff..'' (just so Du know)
Amu had many moments with Ikuto, I don't remember if they all where there in the Anime but like..
link where he tells her he likes her, but since she believes he's just joking she doesn't take him serious, like when Tadase did it.
And there's Mehr scenes like when Ikuto leaves and kisses her, telling her something like,
"I'll definitely make Du fall in Liebe with me, so prepare yourself"
Which were a bold Bewegen to make, but effective.
link <- picture
but well that's a lot of 'moments' but they're aren't the one Wird angezeigt the truth..
it's Tadase himself, when he's in his older version,saying he haven't seen Amu in a long time...
Because Tadase let's Ikuto and Amu be a pair instead of fighting with them about it, since he loves both Amu and Ikuto (as a brother) and realizes that Amu already loves some one else now..
Thou Amu being the easily embarrassed girl she is, blushes a lot no mater if she's interested in a guy oder if he just talks to her.. hehe
when the teacher gets married, it seems like there is a tie, but actually Ikuto already won Amu over, oder Mehr exactly.. Amu were the one winning Ikuto over.. =w='
but he's the one she cries for, the one she's hiding even if the others doesn't like him, because she cares about him.. and do just Mehr than care.. TwT'
And Utau stops chasing Ikuto too, after she and Kukai get's together, and.. Nageshi..ko...? Ugh... what now what's his name x'D ended up with Rima (very cute together I think)
and the samurai guy and Ya..Yu..Yaya? the baby girl? x'D
But well, that's how the story goes, but ofcourse people can look the other way when they like other pairs.. but that's how the Manga ended :'/