I'm probably going to take A LOT of flack for this. Heck, I definitely am, but I have to say it.
In this one page, I think Rain is actually being rather insensitive. At this point, Gavin seems to be bending over backwards for her. He is letting her stay in his room (as we later see), he is walking her all the way to his house, and he's lying right to his mother's face. I know there is probably a significant difference for Rain, but after all Gavin's doing for her right now, I think she should let it slide.
Though I am not trying to justify previous interactions, its just that this one scene seems to suggest this.
Please don't hurt me.