This is really a totally absurd question. Where from are you learning such false axioms. The seventh house potency is what decides your sexual urge together with a powerful 8th house which signifies the genitals. if these two houses are overly potent, multiple marriages could take place or extra marital affairs can be expected. And also read my definitions in Astrology on my blog navagrahastro.blogspot.in.
Extra marital affairs is nothing new in this world and nature permits it too. Just look at the animal world, you can see the proof of this. It is our discipline of the society that prevents such relationship.