"That's how I know. I got really confused when I looked into the trash and found all these boxes from those really bad valentines they sell to kids at the drugstore, but then I... remembered." Gar's brief pause was largely because it hadn't been the boxes that had jogged his memory, but the date. Every year they were together afterwards on that date, without saying why he was doing it, Gar would surprise Rose with flowers or candy or dancing or somesuch.
"But I... loved you too." Another pause. This one was probably quite a bit more obvious.