You know, in the old days an invading force would get a battened down fortified city to surrender by starving the inhabitants into surrendering. They would surround the city to ensure that no outside food can enter. Things get so desperate that eventually the inhabitants start eating each other and the soldiers get too weak to fight. Then they surrender or the invading force thinks they're weak enough to launch a successful attack with little or no resistance.
Now if your wife is starving you sexually, maybe it's a similar tactic. Maybe she's hopeful that by starving you it will cause you to find some "food" elsewhere and when you do so, BAM! "I want a divorce!". She has gotten herself scripturally out of a marriage with an apostate and is free to marry an upstanding elder or ministerial servant.