I had sex on the first date with my SO and we have been together for just over 10 years... fair enough we have had a couple of breaks, but we really do like each other and the breaks have not been long...
We are still together and happier than the early days... We have worked a lot of stuff out during our time together and we are happy to be individuals in our relationship, it is by no means co-dependant!
I don't think it means anything if you sleep with someone on the first date... obviously there is a drive to do such, why not?