Every relationship finds its focus in God. And not just marriages or other romantic relationships but every relationship that exists.
In geometry a focus point is the point in which a curve is defined. Each point of the curve is a set distance from the focus point. It is not always the same distance but there is a relationship in the distance that can be measured by a mathematical equation. And while I am not saying that relationships can be reduced to some sort of mathematical equation, it is this sense of the word focus that I am using. In the same way God is the focus point that defines our relationships with each other.
Let me demonstrate what I mean with a couple of images:
Let's pretend that I can actually draw a triangle.
In this image we see that God is (ignoring my poor drawing skills) the top of a triangle that is drawn using two other people. Think of the points as the people and the line between them as the relationship. The line is the representation of the relationship and not the definition of it. This means that the line is the result of the placement of the points of the people. So when one person grows closer to God the point moves and the lines change.
In the scenario where one person has a closer relationship with God the resulting triangle would look like this:
Notice the length of the line between Person A and Person B. The distance between them grew noticeably longer. (Or it should have if I had any drawing skills.) This greater distance can be very obvious in some instances but not so obvious in others. We also do not usually see dramatic quick changes in relationships like we do between the first and second drawings. It usually happens over a long period of time.
Now this is not to say that you cannot have two people grow closer together without growing closer to God as in the following example:
It is entirely possible. It is also possible for two people to grow closer to God without actually growing closer together.
What I am saying is that it is very difficult maybe even near impossible for one person to grow closer to God and to another person without that other person growing closer to God at the same time. As a matter of fact we see the Bible warning against these types of things.
Paul warns in 2 Corinthians 6:14 about the imbalance found in relationships between believers and unbelievers. And the beginning of Proverbs does so as well albeit in more graphic terms. (I don't know that any of my non-Christian friends have recently said: "Let us lie in wait for blood; let us ambush the innocent without reason.") The problem is that we will aways be separated by one major thing: our allegiance to God. It doesn't mean that we cannot have good relationships with non-Christians. We just need to look at the life of Jesus for an example.
Rather when our relationships with other Christians start to grow distant and our relationships with non-Christians start to grow closer we need to examine our relationship with God. These changes in relationship probably have more to do with our own relationship with God than anything else.