Never said you would cheat on your wife, but there many men who do, after all we are still partly animal and has those instincts still, in animal world there animals with harems and it normal there, specialy the monkeys, have one male leader of several women and few males. He alone rules and sleep the female monkeys, unless on some occassions they approve another male monkey to have some fun with one female monkey.
But yea this is after all a VN and how much ya like sex, unless they nymphos, there is a limit on how much ya have sex, if you young you have more sex in a day then when you get older it slow down a bit, also when you have to work and do house chores, you don't have the amount time to have sex like in this VN.