Even though I felt a tinge of sympathy for the new girl when he all but told her to "fuck off", that quickly faded as I realized what she's (trying) to do here.
The author seems to be implying that he was her only genuine friend, yet at the same time she doesn't really seem to care about him. Despite seeking him out, she wants him to notice her, and ignore his family, friends, and girlfriend to shower her with affection and attention. If she was really willing to be reciprocal and act in good faith, she would have waited for an opportunity to approach him alone, without flippantly bringing up sensitive personal matters (his father), and been honest about her feelings and intentions. But instead, she goes charging-in full of selfishness and entitlement, which shows me that she values him as an emotional crutch more so than a person (if she even really cares about him at all). And unfortunately for her, he subconsciously picks-up on and is repulsed by it.
It really is a shame. The panel where it flashes back to her in middle-school, sitting there alone and crying, while her present self yearns to be noticed, tugs at the heartstrings.
Still, it doesn't justify her shitty behavior, nor make his harsh words any less undeserved.
*sigh* I need some fluff now...