Admittedly I started dancing as a teen then at university so there were a lot of hormones flying around, but there were very few people who managed to keep a boyfriend/girlfriend outside of the society (unless their partner was gay).
The longest-lasting relationships generally were between people both in the society but with other dance partners. There were a lot of dance/romantic partners too, but those would often go wrong, probably because people weren't actually that good a match, but it's very intense, you get to know each other's body and movement quickly, and personal space just isn't really a thing... if the person isn't actively off-putting it's very very easy to nudge from dancing intimacy into personal intimacy. It also doesn't help that you're the only ones focussed on your goal — nobody else cares about your results as much as do.