You overcomplicate this. As an older man who had dated women less than half his age, I can tell you that lust doesn't change much over time, particularly if men go to the gym, life weights, and keep their testosterone levels up. As for the cheating, well, monogamy isn't about how many lovers you want, it's about how many lovers you want your partner to have. If men are satisfied in their relationships, they are loyal. If men are not satisfied in their relationships, their eyes wander, and sometimes, their libido follows. Women tend to be more loyal than men because women tend to depend on men more than the other way around, so women have more to lose from the collapse of a relationship; therefore, they cheat less. Men will cheat for lust, but women generally don't. Women cheat because the men in their lives are so emotionally vacuous that the seek emotional connection with a different man instead of a good orgasm.