Growing up, I learned that the standard for a successful romantic relationship was simple: He asks you to marry him. Get hitched, have kids, buy a house... etc. The be all and end all of mainstream monogamous pairing.
Of course, this doesn't work for everybody. Besides which, it's ridiculous; obviously marriage has nothing to do with whether a relationship is successful or not (except for folks who want to cap off their successful relationship with marriage). But when you take away marriage as a necessary result, or sign of, a successful relationship... what do you use to gauge the success of your romantic relationships?
I have been working this out for myself in the last few days, and I'm very interested in what you think, too!