I'm going to turn down my wife's advances
What do you think will happen when you turn her down all the time?
She will maybe cheat on me with another man
I get that sometimes it is okay to not be in the mood. But you should communicate that too her and tell her why.
Nah, I just want her to go and cheat on me, I don't really think we should be married anymore anyway.
I don't think you should let your sex life define your relationship. You should relax and remember why you got married and the love you have had for her.