I've been married a long time, and i think i can comment on this.
When i was first married there was of course the hot passionate thing.
After a few years had passed that faded a bit, but we still didn't know each other deeply yet. This is the phase where you sort out the things that you overlooked in each other initially, and it can be a difficult time to get through. We both went through quite a bit of "sorting" that did test our commitment to each other. There were times that we could not stand to be in the same room together, but we stayed together anyway, knowing that things would eventually get better.
After a few more years a deeper understanding of each other came. You truly know your partner, and you've seen them at their worst. And you still love them. You have now gone through several of life's trials together with your partner (sickness, death, money issues, family trouble, raising kids, etc).
It is this phase that i'm at now, and it was a long, difficult road to get here. Few make it. But this phase is every bit as sweet as the initial passionate phases. I keep finding new dimensions in my partner that I never knew were there. She puts up with my flaws. I can't imagine life without her.
That's how love works.
