Genetics is a science that is hard to argue with. Sometimes it brings such surprises that parents can’t even recognize their kid, and sometimes all family members look identical: for example, with similar birthmarks or bright red hair.
All of us has different traditions, different cultures, different rituals and other religious practices. Even all the countries have different laws, concepts, and practices. Maybe, things that are normal in your country, are considered extreme in other countries.
A relationship has many aspects. Love, loyalty, understanding, respect can be termed as the four pillars of every relationship. And if even one of these things does not exist, things are bound to fall. Loyalty is probably what keeps the two people together, that sense of being loyal and dedicated to.