Remember your first One? You thought it was forever. You couldn't see a life outside the dream you had. When it didn't work out, it destroyed a piece of you.
The Ones after that were easier. Not roses and sunshine all the time. Just easier. You knew you could survive, even if you had to part. You had survived before during your darkest hour, you could do it again.
Those Ones make you happy, keep your passions running high, but it's only when you find The One - capital T, capital O - that you really know it's going to work. And that's what we're all searching for.