4. If it's worth having, you'll probably have to work for it. (Or fight for it, but don't go starting fights.)
If someone tells you relationships are easy, they're trying to get into your pants. Relationships ask two unrelated people to coexist, often cohabitate, and that is so incredibly hard, it's a wonder anyone's in a relationship at all. This work involves patience (see #2), cooperation, compromise, and communication (see #3). The work is arduous and obnoxious, so it's good the payoff is (generally) worth the work. Don't delude yourself, though: It is a ridiculous amount of work.
Scott Pilgrim could teach a lot of lessons about a lot of things. He's a great model to look to if you want to learn how not to be responsible, upstanding, or not a tool. Through the comics, perhaps more than through the film, Scott learns how the world actually works. It, well, it works. People have to work at jobs for money, bands have to work at their music to not suck, and people have to work at relationships for them to succeed. Some people have to work harder than others, and those people want to date Ramona Flowers. Scott works on relationships in more subtle ways, but the big, obvious one is the wailing on his Ramona's seven evil exes.
5. Some obstacles will seem enormous. They usually aren't.
Have I mentioned that people are generally incompatible? Well, consider it mentioned. There are a million variables making people what they are, and you will never find a person with whom all your variables perfectly align, so stop looking. The object of your affection will always have weird opinions about money, or have a habit that drives you bananas, or be a sexual orientation that isn't oriented towards you. Often, these kill a relationship in its infancy, and life goes on. Sometimes, though, a relationship has everything going for it, but there's one seemingly insurmountable obstacle preventing what you imagine perfect bliss to be like. Guess what? That obstacle probably isn't preventing anything. No one is exactly who you want them to be. Know this, and go be happy with someone you love, despite that part about them you hate.
Mal Reynolds and Inara Serra live together, sort of, and work together, sometimes. More often than not, they're bickering, bantering, and bitching about each other's career of choice. He's a thief, which she has issues with, and he's not too keen that she's a Companion, no matter how revered in society they are. These are genuinely petty when viewed against the obvious love they have for one another, and the good they do for each other as human beings. I know they got together neither in series nor movie, but that doesn't mean they aren't in a romantic relationship in millions of fan fictions, or in their hearts.
6. Don't force something if you're already happy with the way things are.
This seems to go against things I've already said (see #1), but it differs in a slight but vital respect. If you're both happy, and your relationship, as is, is working, don't push to change things. If neither of you wants a label, don't label it. If nobody cares about marriage, why bother? If you're enjoying your sexually tense and exciting adventures, but neither of you feels like you need to define them as anything concrete, there's no reason to do so. Your relationship is your own, and ultimately what makes you happy is what works.
In my mental encyclopedia, there's a sweet little picture of Fox Mulder and Dana Scully next to "tension, sexual." It didn't prevent them from doing their jobs, rather it seemed to enhance their working relationship. It certainly made the series more exciting, and upped the ante on a show where the stakes were already pretty high. The joy of this tension was its lack of resolve; while they eventually jumped into the sack, I prefer the days where no one really talked about it. It was a functional relationship, it made them as happy as it seemed they could be, and it was maddeningly, gloriously without a label.