Wow, GREAT THREAD! TOUGH QUESTION! I would like to go out on a limb and say this. Christians tend to "let themselves go" at far higher rates than the people of the world. In other words, they tend to stop caring about their physical appearance so much. The problem with this is, because God in fact, DID make physical attraction, we can often times become attracted to the people of the world, OVER our own people in Christ. And so, the temptation to mingle with non-believers in a sexual state is there..but is that Godly? No. As 2 Corinthians 6:14 says; "Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness?". This is something that will test your faith in God. Honestly, because you're being joined in Christ through marriage, it is so, that God has set aside a pool of marriage candidates for you called "Christians"; and because of this, since James 1:17 says "Every good and perfect gift is from above, coming down from the Father of the heavenly lights, who does not change like shifting shadows.", then you will know you have found the right candidate for marriage when you feel you can be physically, emotionally, mentally and SPIRITUALLY fulfilled by that person. The spiritual part is important, because although many worldly couples have the physical, emotional, and mental part down, divorce rates are so high because they are not spiritually bonded, due to neither party or maybe even just one party, not hearing from God. Because God made us, he can repair us. Do you take a Lincoln to a Chevy dealer? Do you take a Chevy to a Lexus dealer? No. We seek repairs from the manufacturer. So when we come to him, after seeing our marriage start to drift, knowing that he joined us in marriage, he will repair our relationships. Why do we know he will repair our relationships? Because in his word, he said, as previously stated, "all things good and perfect come from God", and God is not a liar. So if we trusted him to help us find our partner, then when we find our partner, he will not let our relationship with our partners go to nothing, because then it wouldn't be a "good and perfect gift".
So you need the Spiritual aspect of marriage over ANY aspect of marriage; and if you trust God, he will give you every other aspect of marriage and bond them through the Spiritual aspect, making your marriage "Good and perfect". If you are losing physical attraction to your partner you need to talk with God and trust him. Maybe God will change what you are attracted to. Maybe God will help "spice things up" in your marriage to make it certainly more enjoyable and joyous! lol. Maybe God will move on your life or your partner's life and cause them to get in shape, or stop certain bad habits. Just remember, communication in your relationship is NOT between your wife and yourself, or your husband and yourself. Communication, because you're joined by God, is between your spouse, you, and God. When you throw out God, your marriage is almost bound to fail, or bound to have troubling aspects that may never receive any attention. It's like a car with no repairman...the car looks and runs great when you buy it, but over the years, after you've weathered many storms, it's going to need a repairman. Without that repairman, how can your car run properly?