Women know that they will have a husband in the future. So why do they cheat on him by having sex with others?

Okay, Given your expressed limitations, I will approach this another way. In nature, you have no doubt noticed symmetry to be a recurring theme in both form and function. Your argument and logic, conversely, lack symmetry, and fail on that basis. Is that better? Not everyone shares your beliefs, so why would they uphold a standard they may be oblivious to, and do not share?