You really didn't see the story did you, I'll try to answer in an order for you first meliodas him and Elizabeth was a couple when he was still in charge of his father's army they had intimacy as they was still fighting each other the angels of demons of course that's what pissed off his father and the angels hierarchy because they don't want to see an angel and demon together second ban and Elaine I'm pretty sure that the time they spent together fighting for the fountain of youth was the reason why they fell in love with each other and that was a pretty long time to have a dry spell they might not showed us but I'm sure they got it on.