It sounds like you have the same wife-sharing fantasy tens-of-millions of men do. But the fantasy goes away with a little post-nut clarity, like most other men. Obviously you're not ready to share her, and it certainly doesn't sound as is she's into it. Which is all good.....absolutely NOTHING wrong with having the fantasy.
That said, there's nothing about the lifestyle that says the "family thing" HAS to change. It took my wife and I over a year to go from shared fantasy to reality (and probably a year before that for her to fully "buy in" to the fantasy). We have kids, jobs, the whole nine and none of that has changed. We love each other just as much, but with this one "little" thing we enjoying doing occasionally.