Ok, I came to realize this a long time ago. Maybe more than a decade ago. Before I met my wife, I was pretty lonely, I definitely wasn't a 'lady's man'. My friends seem to have better luck in that area. But I realized I was wrong. From the sidelines, I observed that being lonely was far better than being an a dysfunctional relationship. As I watched relationships die, I came to identify these three relationship killers.
#1 You can’t change her/him. You either like the person the way they are or you don't. If they have issues you can't stand, then you need to move on. Do not go into a relationship thinking you can change them. You won't be able to. However, take a self inventory and carefully evaluate why something is annoying you. Make sure that it isn't something petty (although if you can't get over it no matter what, it is never petty, at least to you).
#2 Selfishness. Many arguments are due to your own selfishness; you feel that that there is something you need or are owed. When you realize that, you can actually diffuse the argument. Selfishness is the cause of many petty annoyances I was referring to in #1.
#3 Sarcasm. Don't do it. Do not poke fun at flaws, even if you think you are joking. (this is one that i was really bad at).
I am not trying to make a relationship seem as easy as a 1-2-3 formula. It isn't. It is a complex journey, but one that can be rewarding. Avoiding these three killers is a great step in the right direction.