Marriage, divorce and re-marriage.
The Bible is THE book of relationships. First and foremost, about our relationship with God through Jesus but also about amazing relationships we will have together when we read it and put it into practice.
At the same time, we only have control over what we ourselves do, and not over the lives of others. God also gives everyone the freedom to decide to have a relationship with Him. People can choose to build and grow in that relationship or decide to walk away from God and not pursue a relationship with Him any longer.
Just like people walk away from God, they have the freedom to walk away from each other. Even if they vowed to do otherwise, it is an ongoing decision a person will need to make every day and every hour after they made that initial commitment and vow.
Fortunately, with Gods' help we can be strong and prevent separations and divorces and the damage that occurs because of them. This does not guarantee that in a marriage both parties will continue to seek God's help and grow closer. Both in a situation where only one partner seeks God's help and in situations where a partner stops seeking God's input we can find guidance in God's word.
Ultimately divorce, separation and re-marriage are heart issues and cannot be legislated or managed by anyone. Each situation is different and what may seem at the surface to be easy and even perhaps simple, can be very complex. Only loving, caring and personal talks in a safe environment can help to untangle to complexities and help surface the heart.
The following link will lead to a great study on the subject, with reference materials to consider.
God hates divorce (Malachi 1:27), but he loves great marriages that bring glory to Him and are a beacon of hope to those who are looking for inspiration and hope.