You are right Ellen. It is NOT about sex. It's about intimacy. You can know the mechanics behind every dance move there is, but without intimacy "connection", it's nothing but a shallow moment.. you might as well be playing tennis with your partner on the other side of the court. So it comes down to being comfortable with your partner sharing themselves with others.. at any level. Them being "away" from the relationship, them laughing, joking and mixing with a crowd that you don't know.. ect ect...
I won't say that it is a relationship "problem", but dancing independently may NOT work for all relationships. If it is causing problems in yours, you may have to take inventory of your life and leave behind dance OR the partner..
Brendan