In order for a marriage to be successful, there also needs to be forgiveness. Repentance and forgiveness are complementary gospel principles, and both are necessary in order for us to progress spiritually.
Resentment is one of the worst poisons in marriage. It doesn't ruin a marriage overnight. Rather, it is like decay that gradually and silently damages your teeth. Forgetting to brush your teeth once doesn't ruin your teeth; however, numerous instances of neglect over many years will. Similarly, resentment accumulates gradually, often without us even noticing it. If left untreated, it builds up over a number of years to the point where it destroys love.
Just as our sins and weaknesses are washed away through repentance, forgiveness washes away the hurts and emotional injuries that must be anticipated in being married to someone who is imperfect.