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Fuck it, its a troll, but I have to respond.
Marriage is a bond that implies total devotion of both of the spouses to each other in all aspects of their life - mentally, physically, financially, emotionally, you name it. In a way, a married couple forms a new social "person" in that they act as a functional unit within the society and that they run their affairs accordingly, from a joint household to children.
Now, given that configuration, any infidelity does not even fit within the parameters of what constitutes marriage - any breach of trust by either of the spouses constitutes destruction of the marriage and violation of the bond. As sex is one of the most intense natural experiences one can have with another person, using it for pure entertainment devalues it and lessens the bond between you and your spouse if had with another person.
Now, if you don't value sex as much, it is better that you don't get married, as the institution doesn't suit you and would only cause problems by shackling you and devaluing what most other people aspire to be an ideal form of relationship.