When talking about what's in your heart there's no better place to go than the bible. Because the state of your heart is so important, it is addressed many times. In fact, as with many other issues we face in life, all the answers to this problem can be found there.
My two favorite verses that talk about the importance of this issue are...
Proverbs 4:23 which says, Guard your heart above all else, for it determines the course of your life.
Matthew 12:34 which says, "Whatever is in your heart determines what you say." Or I love how the Message version puts it. "It's your heart, not the dictionary, that gives meaning to your words."
Have you ever said something and later tried to take it back by simply saying "Oh I didn't really mean that." or "Well that's not really what I meant. What I meant was..."? This is what that verse is talking about. It's only a matter of time before what is in your heart to come out in your words and actions. We have a tendency to think thoughts and dwell on things and feelings which isn't always a bad thing, but the problem comes when you think bad thoughts and dwell on bad things. Now lets bring this into the area of your marriage.
When you're married there will come a point when your spouse does or says something to hurt you. You are two human beings living together all the time, it's going to happen. But what you do with those hurts is so important. You have two choices when your spouse does something to hurt you. You can work through that hurt and forgive them or you can store it in your heart and let it fester and grow.
You know the old saying "Let's get to the heart of the issue"? Well that's what we need to do in our marriage sometimes. But a lot of times I don't think the heart of the issue is what your spouse did to hurt you. I think the heart of the issue is simply our hearts. At some point, and often times completely unconsciously, our heart gets turned away from our spouse. They can do something to hurt us and instead of choosing to forgive them we hang onto it, we hold it and store it up in our hearts. And when you do that you bring nothing but harm to your marriage.
Luke 6:45 says "The good person out of the good treasure of his heart produces good, and the evil person out of his evil treasure produces evil, for out of the abundance of the heart his mouth speaks."
What treasure do you have held in your heart towards your marriage? Is it evil or is it good? Whichever one it is, that's what it will produce in your marriage.
So what do you do if your heart has turned from your spouse and you've let things fester and grow? Again, let's go to the bible for the answers.
Proverbs 23:26 says "My son, give me your heart, and let your eyes observe my ways."
The very first thing you have to do is give it to God. You have to give all that hurt, anger, and resentment to God. He already knows it's there, there's no use pretending that it's not. And He's the only one that can help you get rid of it.
The second thing you need to do is get in the Word. He says in that verse "Observe My ways". The bible is full of God's thoughts and His ways to make this life work. He created marriage so of course He has given us the tools we need to make it work. But in order to find those tools you have to get in His word, find them and then put them to use.
Colossians 3:5 says "So put to death the sinful, earthly things lurking within you. Have nothing to do with sexual immorality, impurity, lust, and evil desires."
That's the next thing you have to do. You have to quickly and completely put all those thoughts to death. There is no room to entertain them even a little bit. Thoughts of division and anger towards your spouse do nothing but grow. They will never stay small and hidden. Don't believe the lie that they aren't hurting your marriage! You have to quickly and completely get them out of your heart and your thoughts.
Pslam 51:10 says "Create in me a clean heart, O God. Renew a loyal spirit within me."
I think this is probably the most important part of it all. Anytime you start to feel your heart turn from your spouse and your marriage, this verse has to become your prayer! You have to keep a clean heart and loyal spirit towards your spouse all the time. The minute your heart becomes disloyal towards him/her you open up a foothold for Satan to destroy your marriage. We have to understand that Satan absolutely hates marriage and wants nothing more than to destroy every single one! But I do believe we can do things to divorce-proof our marriages and each of those things starts in your heart. It may seem like an overreaction but remember, "Guard your heart about all else, for it determines the course of your life" and I believe the course of your marriage.
If this is something you struggle with, make a habit of praying Psalm 51:10 over yourself towards your marriage everyday. God already knows the state of your heart and marriage so why not turn to Him for all the help and answers you need?!