Spiritual intimacy in marriage is the bonding that occurs between a husband and wife through their partnering with God, acknowledging His lordship and embracing His will and ways.
Spiritual intimacy is like weaving three strands into a single cord (Ecclesiastes 4:12b). These strands are the husband, wife, and God; with God being the center.
This presentation by Elizabeth Akinsola gives great insight into this topic. Click to download: Spiritual Intimacy in Marriage