This is a case of Mental Harassment as your friend’s wife is mentally torturing him.

Mental torture, also known as psychological torture, is torture that does not cause directly cause physical violence or injury to a person’s body. Forms of mental torture include but are not limited to Isolation: Including solitary confinement. Debilitation: Food, water and sleep deprivation; extreme temperatures.
Mental harassment or emotional abuse is any type of non-physical attitude or behaviour that intimidates, controls, condemns, punishes, humiliates or isolates another person through humiliation, fear or degradation.

Mental harassment against the husband by the wife and in-laws can take the form of the following: constant belittling regarding physical appearances or employment status, subjection to anger and rage, or. having an extra-marital affair or an adulterous relationship or about sexual dissatisfaction.
As per the law being harassed by wife or getting blackmailed can be amounted to Mental Torture.

Mental Torture is a valid ground for divorce under section 498 IPC. Section 498 of the IPC Act is the governing law for mental torture in India among married couples. So, you can suggest your friend to apply a petition for divorce against his wife. But I would suggest you to advise him that he should first confront his wife about this and should try resolve the matter without taking any legal help.