I really liked Ben Affleck's acceptance speech at the Academy Awards ceremony this February. In accepting the Oscar for best picture, he acknowledged and thanked his wife, actress Jennifer Garner. He told her that while their relationship has taken a lot of hard work, there is no one he'd rather work with. Truly great, committed relationships do take continued awareness about yourself, the other person, how you treat each other, and how you can repair things if they go off track.
Great relationships are a little like great houses. You can't buy a beautiful house with a terrific yard, move in, and not repair or fix anything for 5, 10, 20 or more years and expect to have anything of value. Both houses and relationships take regular attention, care, and repairs when things aren't working.
All couples are going to disagree at times. What matters most is being able to repair the problem. It helps to stay solution-focused. Avoid blame. Describe what you observed, as neutrally as possible, and explain what would work better for you next time. Apologize for any ways in which your behavior, thoughtlessness, or reaction made the situation worse. Ask what you could do differently when a similar situation arises again. (It probably will; most couples have patterns). This should help your partner be less defensive with you, too.
Both people in a relationship need to share responsibility for making repairs. I don't like to see the responsibility always resting with one partner, while the other one stubbornly refuses to ever take initiative for a repair. That's not fair, and it will eventually burn out your partner and breed resentment.
I also consider it a danger sign when couples don't speak to each other for days when they have had a fight. This 'deep freeze' is often very painful for one or both partners, and is actually a very wounding and passive-aggressive behavior. It's perfectly okay to cool down when angry, decide you will meet up and talk it through a bit later, but a day or more of not speaking is a really bad idea.
Try to avoid black and white or extreme thinking when there is conflict between you and the other person. While it is sometimes necessary to cut-off or end a relationship that is toxic or dangerous to you, most healthy relationships do have conflicts from time to time. It's not generally helpful to threaten to leave or end the relationship every time you hit a speed bump. The conflicts, if worked through in a respectful way, can actually deepen your connection and understanding of each other.
Choosing a wonderful house to live in, or a terrific partner to share your life with, is a great start. The happily ever after part often depends on different skills, which definitely include attention, care, maintenance, and regular repairs as needed. Think of it as protecting your investment.