Do you trust your partner?
Are you paranoid that your partner may hook up with some random person given the opportunity? People are attracted to excitement and in those moments when inhibitions are lowered and there is a spark it can override a person's customary caution and in one foul swoop change everything. Of course, there is the person who thinks, I am smart enough not to get caught out and maybe that is true and if the now is more powerful than the past, it is entirely possible he or she will be unfaithful given the opportunity. The idea of living for the moment and that right now is all that exists and only do that which makes us feel good is alluring, but it can actually ruin people's lives, living for the moment is the reason people leave marriages.
So how does this affect a relationship or what is the driving force to take a chance on a one night stand when you are involved in a permanent other relationship. The truth is this type of casual sex is only meant to temporarily satisfy an immediate need for sex.
You could get hurt if you sleep around, or you could have fun and enjoy yourself for that night and then let it go, with no regrets.
One night stands are not for everyone.