Summer of '42 (1971) on Netflix

Hermie, in middle age, reflects on the summer of 1942 when he was fifteen, the Americans had recently entered fighting in World War II, and he himself was just entering puberty where thoughts of girls were top on his and his friends' minds. He and his two best friends, Oscy and Benjie, and their respective families, spent the summer on an island off the coast of New England, Hermie the sensitive one, Oscy the forward one, and Benjie the meek scared one still closer to being a child than an adult. Although Hermie and Oscy attempted to get as far as second base with girls their own age, they didn't really comprehend the full act of sex, let alone protected sex, only reading about intercourse and seeing the pictures in Benjie's parents' medical book. As they contemplated perhaps trying to go all the way with girls their own age, Hermie could not stop thinking about the young war bride on the island, Dorothy, her husband who was just shipped overseas into combat. Hermie, who did whatever he could to spend time with Dorothy, had no expectations of her in that manner, as he wanted their friendship to be grown-up yet classy and as she only saw him as a nice young man who sometimes helped her with chores she couldn't manage on her own. But an event that happened in her life would change the nature of their friendship, if only for a brief moment in time, out of emotional necessity.