It's no secret that marriage is a constant work in progress -- you have to keep nurturing it with trust, commitment and lots of communication. If you let any of the following unhealthy relationship behaviors set in, they can undermine your bond. Make sure you're not guilty of these:

1. Growing too far apart

If you're both so busy with work, the kids and your own interests that you hardly have time for a real conversation, you risk becoming too casual about your relationship. Don't take your marriage for granted; make it a point to schedule date nights to reconnect. A University of Virginia study found that couples who spent couple time together at least once a week were 3.5 times more likely to report being very happy in their marriages compared to those who don't make time for each other.

2. Avoiding the problem

If you are unhappy with something, let your partner know how you feel -- just be sure to do so in a calm and rational manner. Don't keep mum just to avoid confrontation. "There's a reason why it is good to 'nip problems in the bud' -- it's so they don't grow into full bloom!" says relationship expert, Lissa Coffey. If you withhold your true feelings, these unresolved issues are likely to come up again and again, and you also risk harboring resentment toward him, which is never healthy.

3. Too tired for sex

Sure, there's much more to a relationship than just sex but you risk losing intimacy if you make no effort in this department. If your busy schedule is making you too tired for sex at the end of the day, find time when you do have the energy and desire for sex -- whether it's in the morning, or the weekend afternoon.

4. Unwilling to say "I'm sorry"

Do you always wait for your partner to make the first reconciliatory move after a fight? Many marriages fall apart because one or both partners are too prideful to take ownership of their mistakes or they push the blame to the other party. These behaviors will slowly but surely create hostility and put a wedge in a relationship. If you have made a mistake, it's important to assume responsibility, apologize and fix it. "It takes a mature and confident person to admit that they are wrong and know that they will still be loved and accepted," says Coffey.

5. Holding a grudge

The inability to forgive your partner for past mistakes means that you haven't really moved on. "Holding grudges is a sure-fire recipe for failure," warns Coffey. The only way for a marriage to heal is to learn to move on as a couple. If you can't get past it, all the negative energy that's bottled up is eventually going to wear down the relationship.