In 7th grade, Peeta realised he had a crush on Katniss. It was a gradual realisation, an accumulation of everything he had known.
In 8th grade, it was obvious to him that Gale, Katniss' best friend, had a crush on her too. That's when he realised he had no chance.
In 9th grade, Peeta finally plucked up the courage to ask Katniss out. He suspected that she agreed out of pity rather than anything else. Gale glared at him every time they passed each other in the corridor.
In 10th grade, Peeta realised he had a crush on Gale. This wasn't a gradual realisation; it hit him with the speed of a train wreck and left him breathless. He and Katniss broke up that year.
In 11th grade, at a school dance, for which neither Peeta nor Gale had a date; he asked Gale to dance and received a yes. He smiled and Gale grinned back and he knew everything was in its rightful place.