Someday We'll Know

"Someday we'll know if love can move a mountain
Someday we'll know why the sky is blue
Someday we'll know why I wasn't meant for you
Someday we'll know why Samson loved Delilah
One day I'll go dancing on the moon
Someday you'll know that I was the one for you"
- "Someday We'll Know"
The New Radicals

We met on New Year's Day, while I was a senior in college, and he was stationed numerous states away in the military. We tried at the long distance thing for about a month and a half, spending long weekends together. My plans for the immediate future were vague - I didn't have a job lined up after graduation, and it didn't seem out of the question that I could consider moving to be where he was.
Valentine's Day came and went, with him sending me a dozen roses accompanied by a card that conjectured about our possible blissful future. The next weekend when he visited, he called it off, citing confusion about his state of life and an unwillingness to continue the relationship. He still wanted to be "friends."
It was like clockwork - each time he moved, he would want me to visit, and I, still wishing for it to work, always did. We had a great time together - we had many similar interests, and a strong physical connection. I could not turn it on and turn it off the way he could - every time I left him I felt somehow that things would turn around. He would change his mind and we would be together again.
This pseudo-relationship continued for about a year, until I was preparing to move out of state. I planned to see him one last time before I moved, and he lived about halfway to where I was headed.
This was it - we had dragged out a year of semi-feelings, and I was ready for change. Evidently, he was, too. While I was staying with him, he met the girl he ended up marrying that summer.
Looking back, I asked myself time and time again - why didn't I make a clean break? It was clear from the first time we broke up that I wasn't the girl he was looking for. So why did I expect that to change?
I have never made a clean break in a relationship. It is always rather a murky transition from relationship to psuedo-relationship, then sometimes to friends.
Last night, I was watching a TV show in which two of the characters were together over 20 years ago. They have failed to make any relationship stick during that time, yet the concept is always in the background.
Why is it that we hold onto these ideals until the other person becomes unavailable?

If it wasn't right the first time, why do we expect that something can change, and it will work later on?