This is a bit of a shameless plug for the book I'm reading right now, but if you want to gain some insight into the long-term potential of your relationship (or insight into a lot of things, really) you should pick up Blink by Malcolm Gladwell. It delves into the instant judgments we're capable of making and how those gut reactions can sometimes be more accurate than judgments made after months of study.
In the first chapter, Gladwell recounts an experiment performed to determine if the success of a marriage can be predicted. They filmed couples discussing their marital issues and analyzed the emotions they displayed. Turns out the designers of the study were able to guess with about 90% accuracy whether the relationships were doomed or not, just based on the ratio of negative interactions to positive. Is that not amazing?
Apparently the number one indicator of a relationship that isn't going to last is the presence of contempt during those conversations. Feeling contempt from the person you love doesn't just affect your heart, but it can lead to more frequent illnesses (!) and less happiness in all areas of life. To me, this makes so much sense. If my boyfriend is upset with me; if we get to the point that we're being mean or calling names, it guts me and makes it nearly impossible to focus on anything other than those negative emotions.
So if you're approaching the point in a conversation or conflict where contempt may enter the equation, step back. They say, "Sticks and stones," and all that, but unkind words from your SO can physically hurt you. And, at the very least, they point toward a predictably grim future for you, as a couple.