Studies have not only been done on humans, but also animals to help prove this theory. For example, the difference between the sexual behavior in montane voles and prairie voles is due to where the vasopressin receptor genes are located in their brains. The receptors for prairie voles are located in proximity to the brain's reward center causing them to remain in monogamous relationship. Where as in montane voles the receptors are found in the region associated with anxiety and fear causing no attachment to be formed to their partners. Experiments showed that it was possible to make a montane male vole act monogamously by increasing the number of vasopressin receptors in the brain's reward center. The same goes for female voles except by increasing oxytocin receptors instead of vasopressin.
Although, the studies prove that infidelity may be caused due to certain hormones it is still a choice. The article even states, "Correlation is not the same as causation; there are undoubtedly many unmeasured factors that contribute to infidelity." From this it can be concluded that some people are more wired to cheat, but this does not mean they can use it as an excuse.