[zeando]

Originally Posted by Vallen Chaos Valiant

Courtly love, perhaps. He wants to make her happy, but he does not have the power to do so.

Spoiler for minor spoiler on Hanekawa:

Eventually when Hanekawa got better, and told him she loves him, Araragi told her he is happy to hear that, but he has someone else. Essentially by the time Hanekawa became romantically acceptable Araragi already pledged himself to crab. Thus, what made the difference is Hanekawa's unresolved "problem".

mostly this, since also hitagi had a problem, but in her case it was ok to stay with her and slowly cure it after the first treatment, while with hanekawa it wasn't

one explanation is, as you said, araragi wasn't really able to solve hanekawa's problem by himself, he had over 2 chances to address it and in both he only solved it temporarily, never definitely
but there may also be other explanations,
he may have been able to solve it, but didn't have the will to do so, in which case one should ask/wonder why he didn't want to
maybe he really wanted to be asked for help by her

Originally Posted by Vallen Chaos Valiant

Keep in mind that he had to re-evaluate his entire view of her, as she is NOTHING like what he had imagined. Whatever feelings he had at the beginning is irrelevant as it is based on love for a girl who doesn't actually exist. What feelings he has now is for the real Hanekawa. The girl who doesn't want to be helped, and refuses to help herself.

instead of saying araragi loved an hanekawa who didn't exists, i would say araragi loved/admired(greatly) only a part of hanekawa(the perfect white one), not her as a whole

Spoiler for an other spoiler from kizu:

but even in kizu, he still considered hanekawa as a friend, so i don't think it's really a matter of him losing his love for her, or getting discouraged once he discovered other sides of her
i think instead it was his feelings for her which never developed to the romantic love stage, and got stuck in the admiration/feeling indebted stage
one way to see it, even if it's very cliche, may have been he didn't want to risk to lose his first real friend he was able(or forced lol) to make