Sometimes he wonders what he's feeling. Like when he's staring at his amazing songwriting best friend and thinking "wow she's gorgeous". Or when he's watching her chew her hair and fret about whatever her latest dilemma is and thinking that it's the cutest thing he's ever seen. He knows he shouldn't feel connected to her but he is. They're tethered. Best friends. Partners. They're everything to each other.
But even the mighty fall sometimes. One of the worst things Austin has had to see is Ally getting turned down by Dallas. Dallas, who doesn't deserve someone as unbelievably perfect as Ally. So when she runs into his arms after Dallas tells her "no I would rather not go out with you" he holds her there and lets her cry her eyes out. And only after she's fallen asleep and he's tucked her in on the couch does he march down to the library (he knows how much Ally hates liberry). And as he's socking Dallas in the facing for hurting his girl it's only then that he realizes he loves her.
That's the thing though. She's not his girl. At least not yet. He wants her to be though. He wants them to be Austin&Ally because I mean we all know it sounds so much better than Ally&Austin. All he wants is to be Ally's guy. He just has to tell her first.