Is divorce a sin if no one was unfaithful?

How can God restore a marriage if the marriage partners believe you can remarry and they run into a new relationship?

I believe if a husband and wife cannot live together, they should seperate and remain single and thus GOD has the ability to restore their relationship.... but if they jump into a new relationship.... it's impossible for even God to restore them.. this is why I do not believe in Remarriage.... if you are sitting there lonely and your partner is making a change in their life you will be much more inclined to go home and restore your home......