It is not unrealistic at all. It just goes to show that Viraj did not feel the need to hide his real face to Jhanvi. He started his abuse of her from the first night, in a psychological way (drinking the cockroach) and that furthermore develops into a physical abuse!
And realising the craziness of her husband, she gets the guard to open up the door and makes a run for it.. only to be caught and him punishing her by burning her feet. For a girl like Jhanvii who was very lively one slap should have been enough to make her run away!
An abuser doesnt waste any time in abusing his victim!.. Like mentioned above Viraj knows how to play Jhanvii and he knew beating her up wont make much of a difference because he has cut her off from the outside world. Hence the fact that the abuse started this early is not unrealistic nor surprising for someone as crazy as Viraj!