As a teenager I understood why Gale was more hateful and resentful than Peeta. He did have a tougher upbringing, after all, and his father died in the mines when he was only 13, and he had to assume the position as head of his family and put his name more times in the reaping. On the day of the reaping for the 74th Hunger Games, his name was in 42 times, whereas Peeta, for reference, likely only had five entries.
And yet by the end of the series — by the end of the first book, even — Peeta had arguably gone through worse than Gale. For all his entries, Gale was never actually reaped. Didn’t have to go into the Games, fight for his life in a sadistic, controlled environment, or forced to kill other people. Never lost his leg, a disability no amount of childhood privilege can make up for. Gale never lost his family in a bombing, and was never hijacked and tortured by the Capitol.
Despite it all, Peeta didn’t let any of that turn him bitter, or dull his sincerity and compassion. He didn’t take his anger out on Katniss like Gale, or act huffy when she didn’t immediately love him back. He simply loved her, purely and genuinely and passionately, until she loved him back. Enthusiastically, out of her own free will.
I think it links to a larger argument about privilege and virtue. Suffering is tough, but it’s not inherently virtuous. Peeta was more privileged than Gale, but he was still District, after all, and eligible to be reaped. And he could have chosen to let his horrible experiences plunge him into a rage and anger — and RIGHTFULLY so! — but he chose otherwise. He chose love, and hope.