Angelina has always liked the Weasley twins, but she especially liked George. When Fred asked her to the Yule Ball, she couldn't turn him down, even if he wasn't the Weasley she had her eye on. After all, Fred was George's twin, so they weren't much different. Angelina never became more than friends with either of them, but she and both of the twins were very close friends throughout the years.
A few years after the Yule Ball, Angelina, Fred, and George returned to help fight against Voldemort in the Battle of Hogwarts. In that battle, Fred Weasley, one of the funniest boys ever to attend Hogwarts, lost his life. Outside of the Weasley family, no one was more affected by this than Angelina. At this moment, George and Angelina bonded more than they ever had because Fred's death had affected both of them so greatly. The next day was when George asked her to be his girlfriend. She answered with a joyful "yes" and hugged him on the spot, much to his surprise. They've loved each other ever since.