Do loving things for your spouse and your feelings of love will grow.
“Husbands, love your wives, as Christ loved the church and gave himself up for her.” -Ephesians 5:25
The command to love your wife refers to the 'do' of love or the 'verb' of love. So obey God and just do it, give your wife a massage, do the laundry for her, buy her flowers, tell her the good thoughts you have about her, and most of all pray for her daily. I promise you, because the Word of God cannot lie, that He will make those feelings grow that seemed lacking at the time. Your service to her will have the bonus of causing her love to increase as well. The best wisdom I got before getting married was not a warning, it was a command and encouragement from a brother saying, "Keep loving her. You'll love her more and more every year." I thought, that has to be right, Christians are never stagnant and pleased with their amount of love, they always fight for more, and will always have more. So, here's another command from God for Him to enlarge your heart by.
“Let your fountain be blessed, and rejoice in the wife of your youth, a lovely deer, a graceful doe. Let her breasts fill you at all times with delight; be intoxicated always in her love.” – Proverbs 5:18-19
I've always found that the command to rejoice in something is best executed through giving thanks about that thing. For example, if I don't feel happy about my job, I will give thanks and my heart grabs onto the reasons that I'm reminded of. Thanksgiving is certainly commanded throughout scripture. So if you're not having the feelings of rejoicing, then give God thanks for your wife and you'll soon find yourself rejoicing in her. Just think about her lovely form. Think about how she loves you, despite all of your failings! Think about all of her virtues. Think of how she loves God. Think of how she hates the faults she has and is seeking to overcome them.
Whether you are a husband or a wife, seek to love your spouse, and know that God’s Word will not fail you; your heart will be enlarged.