I feel guilty for being an asshole to her, yet I have no reason whatsoever to be nice to her for even a second. That's the thing about being the guy who was always nice to the girl. Even when a good dose of dickhead is warranted, that guilt sneaks in, ready to tear you apart. Ironic, given how she tore me apart.
The narrator expresses conflicting emotions regarding his treatment of a girl who has been unkind to him. Despite his feelings of guilt for acting harshly, he struggles with the idea that he shouldn't feel obligated to be nice after how she has treated him. This tension highlights the complexities of relationships where one party has been consistently accommodating while the other has not reciprocated.
This internal struggle reveals the irony of the situation, as the person he has tried to be nice to has caused him significant emotional pain. The narrator recognizes that even when justified in his anger, the lingering feelings of guilt prevent him from fully embracing that side of himself, illustrating the difficulty of navigating feelings of hurt and betrayal in personal relationships.