Not to seem like a dog with a bone, but I wonder if establishing additional marriages for M'Benga is a prelude to establishing additional children. I still think they're lying to us in promo material about what the name of Ensign Nurse is to cover a reveal, just like with John Harrison and Javid Iqbal.
He definitely killed him, but the way it was staged was meant to offer some narrative ambiguity about which of them actually started the fight, even though it was pretty likely M'Benga was the one who snapped. And even if he hadn't, M'Benga was definitely provoking him to try and get an excuse to kill him.