By the sounds of it wont-stop you are making her decision to leave EASY rather than making it COMPLICATED.
Are you calling this guy her "boyfriend" when you discuss her affair? Don't do that.
Are you letting her feel she can return after she's experimented and tested the waters with this guy? Don't do that.
You just validate her affair, making her decision to walk out EASY.
When I was cheating on my husband he made the decision to continue my affair easy by doing the same things you are.
He made me feel OK about what I was doing, he made it clear he would take me back at any time if I changed my mind.
It just made me WANT to leave, WANT to cheat, WANT to continue the dark road I was on.
Make her decision to exit the marriage difficult for her, make her THINK LONG and HARD about what she's doing.
By the sounds of it you are just handing her off to this guy.
Don't argue, don't fight, don't be mean in any way, but make it abundantly clear to this woman that her affair is a ONE-WAY ticket only, there is NO RETURN TRIP.
