Make that a cup of trust and loads of intimacy!
As long as Mr. Man can live with himself, I am good to great when it comes to the understanding of an open relationship. It's both a learning and aging process on the journey to building companionship.
That said, no one written rule or trumped up formula will work for everyone.
The bottom line is simplicity.
The middle ground is communication and compatibility
To top of it all, unfettered selfless access to freedom and growth.
At the end of the day, not because a man or woman wants their freedom, it necessarily means they are going to act on having multiple partners!
Not knowing or trusting each other will definitely lead to the heart break motel