I have no idea whether this same practice exists in other cultures around the world but in Bhutan, it’s generally acceptable to have an affair with or even marry the sisters of our spouse. We call them Mathangs (sisters-in-law) and we don’t share ethical boundaries with them. We can freely joke with them, tease them and even marry them if deemed necessary and appropriate. Since we are related only through marriage, we don’t hesitate to open up ourselves to each other and the society accepts it. But in Lhotsham culture where I come from, there is a slight distinction between the spouse’s younger sisters and elder sisters and there is a strong logic behind this distinction.
In a Hindu society, we can flirt only with our wife’s younger sisters because they are our real Mathangs in the actual sense of the term. But with the elder sisters-in-law, we must be respectful and disciplined. They are considered equivalent to the parents of our wife and hence, they deserve the same kind of respect we owe our parents-in-law. Traditionally, we cannot even look at their eyes directly and have to bow our head down wherever we meet them. We are not allowed to touch them physically even while handing or receiving things from them or while crossing over each other on the way. Because of this strong cultural practice, I have to be always careful when I am in my wife’s home where I have to maintain a safe distance with her mother and elder sisters.
Now what makes our elder sisters-in-law more special than their younger sisters? Why do we respect them more than our younger sisters-in-law? Well, there is logic behind this tradition. It’s generally believed that as elder sisters, they would have definitely shared the responsibilities of their parents to look after your wife when she was a child. They would have taken care of your wife just like her parents starting from feeding her and changing her cloths to guarding her against external dangers. This is the main reason why they have to be honored for their love and care for your wife when she was their little sister. That’s why we address them as “Jethri sasu” which means “elder mother-in-law” and we respect them as much as we respect our mother-in-law for all the care and love they had given to our wife during her childhood.
Likewise, your wife would have also done the same thing to her younger sisters. As an elder sister, she would have looked after them like their parents and hence, she does not literarily owe them anything. It’s for this reason that you don’t have ethical boundaries with them. Since they owe your wife respect and gratitude, you are culturally allowed to mingle with them as long as you don’t get too far to hurt the sentiments of your wife. So this is the main logic behind why we treat our elder sisters-in-law differently from younger sisters-in-law. In Hindu culture, it’s very important to understand this distinction so that we can deal with the situations in culturally appropriate manners.