I would'nt be too hard on those that stick to themselves. When we started out we were much like that, dancing together and being very nervous when ever anyone approached us. It took us a year before we met a couple who made us comfortable enough to get started. That was 4 years ago.
But during that year when we stuck together we did enjoy ourselves. The sexy atmosphere and the feeling of naughtyness fueled many a good night between us. Of course now that we are right in the swing of things it's even better.
It just takes some couples more time to get involved. Let them advance at their own pace.
