Do not deprive each other except by mutual consent and for a time, so that you may devote yourselves to prayer. Then come together again so that Satan will not tempt you because of your lack of self-control. 1 Corinthians 7:5
Sex is the superglue of marriage. But the Bible never says how often a husband and wife should have sex. It does, though, tell us that it is unhealthy for a couple to abstain from sex for an extended period of time. The break in physical intimacy only allows Satan to infiltrate the marriage with temptation. This passage does give one specific reason to abstain for a time, but both husband and wife must agree. The one reason is prayer. Praying together draws you together with your spouse emotionally and spiritually. This emotional and spiritual connection will, in turn, lead you back to a time of physical connection.
If you are consistently too tired or too busy for sex with your spouse, consider the words from the passage above. They are still applicable today. As you move forward together, continue to pursue your spouse. And discover that the marriage God has in store for you is all about lasting intimacy and connection for the rest of your life!