Danger zone.
Cheating isn't swinging, but you know that.
Enjoy the flirting and teasing, until she resolves the problem on her own with her husband or they come to an agreement that she can play without him. I seriously doubt that will happen by what you say of him.
If you come out to him, expect it to be spread far and wide that you're swingers and worse. Then the fun friendship is over.
Mr. & Mrs. D