Well, I'm glad to hear that it isn't necessary for validation.
It's not necessary for validation, but it provides validation when it happens. It tells the man "Yes, you're acceptable. You make the grade." Having one's advances rebuffed, particularly in the framework of a stable relationship, sends the opposite message.
Why do rebuffed advances have to be interpreted as a lack of validation? Maybe your partner is just tired and stressed or PMSing majorly at that particular time. It doesn't mean that they don't value you or love you (unless you are getting rebuffed a lot).