Phil George explains in this video that it is important for a marriage to cultivate encouragement. It can be helpful for both spouses to encourage and demonstrate appreciate each other. It is also helpful to be servants of each other. Oftentimes, it can be easy to become complacent in marriage and take each other for granted which is why it is important to keep this idea in mind.

1 Thessalonians 5:11 (NKJV) - "Therefore comfort each other and edify one another, just as you also are doing."

Something very helpful in keeping your marriage sweet is having your marriage be one that has an atmosphere of encouragement. There's so often that we think thankful thoughts in our heads, but we're just really not good about actually communicating those to others particularly our spouse and so whether that's things like texts or emails, notes, letters or face-to-face be faithful in encouraging each other in your marriage. Be faithful in encouraging your husband when he is faithfully trying to lead family worship. Be faithful in encouraging your wife when she manages to get dinner on the table while also managing a house full of kids. And also be faithful in serving one another.

The biblical principle is that feelings follow actions and so as we lay down our lives and pick up our cross and follow Christ and serve our spouse in a self-sacrificial way that's going to be something that just continues to happen in a realm of sweetness rise up from within our marriages.