S.O.S.

I was reading an article in the Guardian, a British newspaper (see the link below), and had trouble understanding the following sentence:

“He had been arrested at least twice for threatening violence against the husband of a man whose wife he was sleeping with.” 

Mimimally, these questions ensued: Is this a man-man-woman or man-man-man threesome marriage? Why does "He" (Poulin) threaten "the husband of a man" rather than "a man whose wife he was sleeping with?" How to interpretate this grammatically corrent but semantically incomprehensible sentence? I've sent a request to the Guardian and nothing returned yet. And I'm getting impatient because I'm dying to know what really happend with Poulin's sexual saga, which may have contributed to his decision to join ISIS. Can anyone help? 

http://www.theguardian.com/world/2015/mar/09/how-isis-attracts-foreign-fighters-the-state-of-terror-book#comment-48640163

Lostalley
03/09/2015, Maryland