Polyamory

It seems to me that many couples that come to be Poly start out as a result of infidelity or one partner's having met someone they wish to pursue a relationship with, but want to do so 'without guilt'.

Is this the norm?

I struggle to imagine how well a poly 'primary' relationship can stand up to that, being the 'betrayal' of it's inception.

(This is just an observation I've made on the 'net in general... I could be wrong about how often it happens )