Nights were dark, and Laban was sneaky. So far as I can see Biblically, when a couple (Man, and Woman, present mores not withstanding) join flesh - they're married, and any subsequent sexual activity with anybody else constitutes SIN.
In the U.S. I wouldn't be surprised if the majority of "weddings" are performed between people who've already been MARRIED, maybe for years, and probably already in multiple adultries. A "Wedding", and all the accompanying hoopla, is nothing more that the formalization of a civil contract between two parties, and really has nothing to do with an actual "Marriage".
Rules about marriage were relaxed in the OLD Testament, since people had no indwelling Spirit to affect their actions.