I'm with you, if it's a good fit it'll last because neither person can face the idea of it ending, when you define things and try to crowbar them into these metrics of a relationship you're just runing the fun. that's why I'm never getting married, I'd be thrilled to meet a woman that I end up happy with and never get bored with for the rest of my life, but it's idiotic to promise that I won't get tired of her after only knowing her a couple of years, people change they grow apart I'd essentially be lying because there's no possible way to know how we'll feel about each other in 10 years