My first relationship ended the day before our wedding was supposed to take place, 8 years after we started dating. It was a heartbreaking break-up, that I recovered from much quicker than I would have thought...the further away from the situation I was, the less I missed him.
Then, one day, I realized what an awful person I was in that relationship. I was selfish, dominating, controlling, critical... I was a lot of things I wouldn't take from anyone, and never wish to be again. But without our r-ship to bring those awful things to the surface, I would not have been able to make the changes I have made.
However, I learned about him, too. I learned to trust what a man does, not the pretty things he says (this guy wrote excellent poetry...without it, I'm sure the r-ship wouldn't have lasted as long!). I learned that no guy can make you happy--only you can do that for yourself. I learned that no one is perfect, but that doesn't mean you have to make compromises on what you want. If you don't want a man who is addicted to sports, find one who likes something else (there's a lot to choose from: you've got cars, video games, technology...etc.). I didn't realize that it was ok to NOT settle.
Basically, all relationships will eventually bring out the worst, most selfish parts of you. But there should be enough positives brought to the surface to make it worthwhile.