Marriage as an institution has become more of a legal contract than a religious ceremony. Since marriage is a contract, the involved parties, i.e. the spouses can decide to break the marriage and go their separate ways.
A divorce has many legal implications involving property ownership, child custody and other matters. The state gets involved since properties have to have legal titles and the proper care of children is another legitimate legal matter.
Separation can happen in many ways. It can be amicably settled between the spouses themselves,