When you have a relationship with a man/woman, it's with this individual, not with every single other human being on the planet.
If I'm not with anyone and I try to seduce your girlfriend, it's HER job to say no. Unless you don't think she is smart enough to make her own decisions. But in this case we have other problems...
As opposed to jetti, I'm not sure the wife would just have found somebody else. But regardless, she was the one in couple with the boss.
I'm confused by most of the reactions I see here. It's as if they expect the boss to be able to tell employees who they can fuck.
Kudos to this boss for at least considering that firing the guy is not the only solution.