I want to point something out: I'm glad I waited on marriage. I'm glad I got to learn about how this whole relationship thing works before making it an actual binding contract. In the time I've been with Kobi, I've seen a lot of couples split and although we weathered the storm, it wasn't always easy. We had to learn so much to make it work.

Here's what I've learned about what makes a lasting relationship tick.

Trust
You can't have a lasting relationship if you can't trust someone to be left alone, or if you're afraid they won't come back to you. Period. I've seen it time and time again: relationships where partners are suspicious of each other fall apart rapidly.
The Fix
If your partner isn't trustworthy, just end it. Save yourself the pain. If you're not sure if your partner is trustworthy, give them a chance to show you whether or not they can be trusted, even if that means making yourself vulnerable to betrayal, and treat all breaches of trust as a serious problem because they are. If your partner is trustworthy but you can't bring yourself to trust them, work on yourself because you're either too insecure to keep a lasting relationship or you're untrustworthy yourself and projecting.

Honesty
Some people say it's healthy to have some secrets, but I find that when you get in the habit of keeping secrets from someone you're supposed to love and trust, you're basically sitting on a time bomb. Sooner or later, after you've been seeing someone a while, especially if you live together, secrets will come out and there's nothing you can do about it. Better to avoid that day of reckoning altogether.
The Fix
Have as few secrets from your partner as possible. If they can't take the honest truth of who you are, you either need to find another partner who can accept you or you need to really work on yourself, depending on the issue at hand. Radical honesty is liberating, but such a rare virtue.

Respect
I've seen a lot of relationships that go something like this: Boy meets girl. Boy is a furry; girl is not. Girl objects to boy being a furry. Boy tries to be what she wants him to be. Two months later, he's sick of her. It doesn't have to be furry status though, or a hetero relationship; it can involve favorite music, disability status, taste in clothes, taste in food, national origin, race, religion, or any number of things that make a couple diverse. Or it can be a simple matter of someone holding their partner in a generally low regard for no obvious reason; that's all too common from what I've seen.
The Fix
Get over your hangups. Respect the differences of those who love you. Find common ground and allow your partner to be themselves because people who aren't allowed to be themselves will eventually get sick of having to be someone else to please you. And if you're involved in a controlling relationship where someone is trying to make you be someone you're not, have some self-respect. Stand up for yourself and don't be forced to become someone you're not; make it clear that you're not going to be intimidated into being someone you don't want to be. And whatever you do, NEVER stay in an abusive relationship because abuse is what happens when a person doesn't respect you. If you are unclear about what an abusive relationship is, just do a bit of searching on the subject! There are plenty of good resources out there. A general rule of thumb, though, is that if someone consistently makes you feel bad about yourself and goes out of their way to degrade you, it's abusive.

Communication
Relationships often break down on this point. Partner A assumes that Partner B wants something, or knows that something is bothering them. They discover that Partner B didn't know and they get indignant about it. An argument ensues, then reconciliation. The cycle repeats often. The relationship usually breaks down slowly and painfully (though a rapid breakdown is possible too).
The Fix
NEVER ASSUME. Tell your partner when something is bothering you, even if you think they should already know. Tell your partner what you want, even if you think they should know. Ask your partner what they think, what they want, or how they feel, even if you think you know them like you know yourself. Make it clear to your partner that you are ready and willing to talk about the things that matter in your life. Discuss your plans, hopes, dreams, fears, concerns, problems, and all these little things that are too important to leave to chance.

That's it really. These four things are the absolute, most important things anyone in any relationship needs to know about and hone if they want their relationship to last a long time. They take a great deal of time and patience to learn and they have to be constantly and vigilantly maintained or you'll risk falling into bad habits and making your relationship go sour.

Good luck, and may you find true love!