I think it's definitely a girl/girl song, and the more I think about it, the more I think the "relationship" is almost entirely imaginary on the part of the singer. The singer is the stalker-y one, but she justifies her own obsession with the idea (which I take to be entirely in her head) that the target it obsessed with her. She's not actually calling her, looking for her, or following her with her eyes except in the sense that she's keeping track of the crazy chick's movements.
And "the trouble after high school" stems from some public altercation that made "him" think the target actually was cheating on him with the singer.
I think it's definitely a girl/girl song, and the more I think about it, the more I think the "relationship" is almost entirely imaginary on the part of the singer. The singer is the stalker-y one, but she justifies her own obsession with the idea (which I take to be entirely in her head) that the target it obsessed with her. She's not actually calling her, looking for her, or following her with her eyes except in the sense that she's keeping track of the crazy chick's movements.
And "the trouble after high school" stems from some public altercation that made "him" think the target actually was cheating on him with the singer.