I can agree with the whole asking for permission trope since that's how the story is written, Kathryn really don't have a choice. With her loving and caring personality, it's not hard to understand why she's so loyal to Luke. Besides, he made her promise to always ask and that they should make decisions together.
It's mind boggling that Luke has the option to have sex with anyone and if he don't, he still feels guilty because he was tempted, but still never says anything to Kathryn.
The way I see this is, it's up to him to keep the path of loyalty in the relationship. But, it appears also, that he fails at every opportunity.
It just makes me, as the player, feel hypocritical or even selfish, in pushing Kathryn to fulfill his fetishes.
Kathryn is beautiful, sweet and adorable. It's hard to even understand why Luke would consider having sex with anyone else. (other than being a douche-bag and the other side of the coin that one woman isn't enough).