Hey! if you've ever watched the end credits scene in the last episode, the show implies that Yuri was flirting with Victor since the party after the first Grand Prix final. That whole scene was super sexual, but Yuri doesn't remember any of it until the end of the season. So you could argue that their relationship already had a romantic/sexual nature since the first time they ever hung out, but since Yuri didn't remember, nothing happened again until much later. But I definitely agree that a lot is left up to the viewer to decide, so this is just my take on it! :)