Compromise

One thing I think happens in long term relationships or marriages that fail is people find themselves compromising for their partners to the point where their own happiness is being compromised. Compromise is something that has to happen to make a long lasting relationships work but each person needs to be aware that although they may not like conpromising, the other person is doing it as well.
Don't hold the fact that you have to compromise against the other person; don't be selfish. Compromise, admit your mistakes, learn from them and do what makes you BOTH happy. If you choose one person to spend the rest of your life with and start a family with, their well being and happiness should be important to you and just below making sure your happy yourself.
 You can't treat someone the way they deserve to be treated if you are holding a grudge, not being honest, or having a one sided relationship. It always takes two to make it work.
No one is this world is perfect, and even if you've found the person that you believe is perfect for you, doesn't mean there won't be times that they annoy you or make you mad. But it's realizing were all human in these times, and even this person you love so deeply can feel the same ways about you. Sometimes its speaking up about being bothered, and sometimes it's knowing it's not a big deal and moving on.
 If your standards are so high that something like a pet peeve or disagreement can ruin for you all the other great qualities a person has, then I believe one of two things needs to happen; there either needs to be a discussion about the problems to create a common ground or a solution. This indeed means one or both people may have to compromise and realize they have the control to change this small thing they're doing that won't negatively effect their own lives, and only make the other person happier with the situation.

 Here's an example of this: maybe the way a woman puts away her husband's laundry is causing the clothes to have wrinkles. The wife does all the laundry for the family and it's hard work, so when the husband brings up maybe she should fold the laundry differently, instead of getting upset that you've been told your not doing something right; compromise.
Take in to consideration it is important to the husband to have a wrinkle free wardrobe, and you are the one in control of that. So just try it, fold the laundry different the following week and see if it helps the problem instead of arguing about it or holding a grudge and assuming his intentions were to put you down.

The other thing that could happen is the realization that there is so much compromising going on that happiness is also being compromised. This is as well a discussion, however it doesn't mean every debate between couples can end with a happy solution.
 If there are so many grudges, annoyances, and disagreements that the majority of the relationship has become negative, then sometimes going separate ways is the only way to let both people be fully happy.

An example of this is usually a more serious matter, or more things built up rather than one or a few smaller issues that are dealt with quickly like mentioned above.
This would be more like having conflicting opinions about finances and how money should be spent despite a tight budget, different lifestyles or beliefs, having hard feelings or holding grudges constantly, or being unable to overcome a betrayal. These are certain things that may not be worth compromising for, if in the end your happiness is compromised.

So in the end, the ultimate choice is yours on what you decide to compromise with. But you should NEVER allow letting go of an issue to cause deeper problems. Know what you want and what makes you happy, and also know what you significant other wants and needs to be happy. It will always take two to make it work.