If you lose your spouse's trust, be willing to work hard to regain it. Allow each other time for personal pursuits. If you can trust one another, then time apart should not be a problem. Fidelity should be discussed. An affair does not have to be the end of a marriage, it can lead to a renewed love affair between husband and wife.
Infidelity is usually a sign of something wrong within the marriage.
Romance should not die at the altar. All relationships evolve. Passion tends to subside. Make time for each other and rekindle the flames of love. Make a financial plan that you both can live with.