1-3: It seems you're using an irrational rule for updating your beliefs about your spouse. If we fixed this minor shortcoming, would you lie?
6: Why not problematic? Unlike your Trolley Problem example, in my example the lie is caused by consequentialism in the first place. It's more similar to the Prisoner's Dilemma, if you ask me.
1-3: It's an alief, not a belief, because I know that lying to my spouse doesn't really make my spouse more likely to lie to me. But yes, I suppose I would be a happier person if I were capable of maintaining that alief (and repressing my guilt) while having an affair. I wonder if I would want to take a pill that would do that. Interesting. Anyways, if I did take that pill, then yes, I would cheat and lie.
The title says it all.