Yeah, I think that it's absurd to believe that there is only one compatible person on the planet for each of us. For one thing, some people have very common tastes. For example, if "I like to watch movies, eat at nice restaurants and walk around the lake." Hey, who doesn't like those things? Odds are, you will have an easy time finding somebody who also likes those things. I don't mean to be dismissive about the concept of love, but it's not necessarily a once-in-a-lifetime deal.
Another example, young love. Two teenagers can certainly fall in love, and experience intense romance. And as they mature and change, they can fall right out of love. It doesn't make them bad people, they just changed and grew up.
Johnfisher, I think that you are setting yourself up for a world of pain if you obsess over love and idealize it to an extreme degree. What if the first woman you love turns out to be a cheater? Or gets hit by a car? Or just can't stand the way you chew your food after a few years together? Things happen. Life is complex. It doesn't matter if you want to keep everything in simple black-and-white terms, we live in a world that is challenging and ever-changing.
All that said, my parents were married for 43 years, until my dad died of cancer two years ago. I've been hoping that my mom wouldn't start dating again, because she is starting to struggle with Alzheimer's. So it was a big relief when she told me yesterday that she still loves my dad and isn't interested in dating someone new.
One other thing. While I believe that people can love multiple times in a lifetime, I don't believe that anybody can feel real romantic love for more than one person at the same time. In those kinds of situations, I think that the two-timer just loves himself (or herself).
Good decisions come from experience. Experience comes from bad decisions.