when I say day dreaming, eulalia, I am not talking about what goes on in your head when you are sleeping. Trying to control my subconscious is going a step too far
I do think day dreaming about a nice man has an advantage anyway - it can raise your libido - and that in turn is a boost for your dh - and you.
But what I was getting at was when day dreaming becomes obsessing. If you spend hours each day fantasising about the object of your desire, think about them when you are making love to your dh, this is no longer a harmless outlet for feelings - it is detrimental to your relationship. And arguably IF you can manage an affair, keep it secret, not expect more than the odd date, the other person in agreement, then your mind is a lot more free to concentrate on your dh.
Turning the tables, if I knew my dh was utterly obsessed with another woman, totally absent when he was around me, struggling with himself to not take it further, bad tempered, resentful, all the time, would this be less hurtful to me than if he had the odd secret rendevous with another woman, no other commitment, and gave all his attention to me when he was with me?
Personally I think it would the obession and resulting damage that would do our relationship, more than a physical fling that I'd find most hurtful.