I’m not into or in an open relationship, nor do I have any interest in changing my very-monogamous marriage into an open relationship.
However, data indicates that open marriages have a comparable divorce/success rate as us in the vanilla-variety marriages.
What is clear though with “successful” open marriages is that it’s an agreement, the agreement is known and there are accepted and respected borders around that agreement.
For example: A couple might agree that there is no emotion, pure sex. There might be limits on financial spending on lovers. There might be a rule on safe-sex, cleanliness and protection. There might be a limit on time spent, frequency of meetings. There might even be an agreement on secrecy and a joint “blind eye” so you pretend to think she really is meeting “the girls” and she pretends you really need to work “overtime”.
The rules are known and both parties are accountable within those rules.
I can’t find your story. I don’t know what sort of affair your wife had. If it was “just” a quick romp in some stranger’s truck or an in/out at a motel then… well… maybe you two could agree on an open marriage. After all the affair was more of a sexual nature than an emotional one (often a prerequisite for open marriages).
But if it was a build-up with emotional attachment, romance and dreams of a future… If it was an exit affair… If it’s still ongoing and she can’t break it off… then offering an open marriage is a lot like trying to call your truck a boat after driving into a lake.
Are you OK with the thought of your wife being with another man if it’s with your knowledge? Will you be fine with going to bed on a Friday night knowing she’s at the Howard Johnson with Ted – the guy she told you about who hit on her at the mall the other day? If you are fine with those thoughts and/or think you two can agree on ground-rules for an open marriage then you could open that discussion with her.
"If, therefore, any be unhappy, let him remember that he is unhappy by reason of himself alone." Epictetus