My grandma was having an affair with a married man (?) and was in the pub with her friends. My grandad walked in with a mutual friend and asked "who's that girl?" Apparently he then decided there and then she was the woman he was going to marry, but I take that with a pinch of salt... They arranged to meet up, but neither of them actually turned up, so the mutual friend went to both of them telling them how disappointed each of them was that the other didn't show up! So they arranged another date, actually showed up, my grandma dumped the married man and they were married for over 50 years.
My grandma's cousin was in a Nazi concentration camp and married one of the soliders who liberated the camp, they got engaged 3 days after they met, which I think is the best story ever. https://www.telegraph.co.uk/news/1399803/Gas-chamber-survivor-found-love.html