Ram,
There are a lot of things to consider before going that route. I can't imagine more than a small number of couples can actually survive and prosper in that kind of an arrangement.
One thing to consider is that women chemically (as in physically demonstrable ways) can become attached to a man they are sleeping with even if the intention is simply recreational. One of the reasons women tend to be more cautious than men in who they choose as partners is because they are aware of this reality within themsleves. They become emotionally attached in no small measure because their bodies are programmed to react that way.
The second thing to consider is the following. Women, whether they want to be or not, are atracted to alpha males. It's instinctive. When you become a voyeur of your own wife doing another guy you automatically become beta in her eyes, even if she swears up and down repeatedly that this won't happen. It's not a conscious choice she can make. She may rationalize it, or try to, but very few people can do so successfully. You don't want to become that in her eyes, and elevate the other guy into your former place. Because even when he is no longer around, she will be looking for an alpha, even if only subconciously, and you will never be able to fill that role again.
That's why so many women have "forced sex" fantasies, or talk about wanting to be picked up by their man and slammed down hard on the bed when they are having sex. They want to be dominated subconsciously, even if they say differently otherwise.
Finally, be certain you can handle the reality. It's one thing to imagine it happening, altogether different when it's happening right in front of you, and she is obviously enjoying it to no end.