Hi Bob,
I understand how disheartening it can be as a single to not be able to find someone to dance with. Many single men and women feel the frustration that you have expressed. However, there are many actions that you can take to overcome this, as was noted by ladydance. As she suggested, a good lead with a kind and positive attitude rarely has trouble finding a partner to dance with.
Are there not any single ladies at the venue you are going to? Or, are you, like so many others, just one of those guys who wants the one you can't have?
Don't focus on the lady's who are already taken. Find a venue where there are singles. Or, better yet, if you are dancing to find women, why don't you try on-line dating and instead of inviting them to the usual dinner and a movie, take her out dancing and wow her with your moves. Even if the relationship doesn't work, you'll have another potential dance partner if she sticks with it.
You also mentioned that couples should stay home for a "date night". It's always a wonderful thing to snuggle up to your honey on the couch on any given night. However, socializing with others is an important part of any couple's relationship. Singles may feel left out when couples socialize together, but it is important and healthy for them to do so. If you are into being a bachelor, find others who enjoy the same lifestyle. Otherwise, look forward to the day when you can join the "couples club"!