TRUE DESTINY

Love is our true destiny. We do not find the meaning of life by ourselves alone - we find it with another. — Thomas Merton

There were several repeated themes to LOST. "Live Together or Die Alone." "Trust Me." "This is your destiny."

If you believe the show was about Jack, then read on.
If you believe the show was supposed to be about Kate, then read on.
Both camps could be right.

If LOST's tangled storyline stew gets boiled down to its essence, what happened to both Jack and Kate in the end? They found each other, again. 

If life's true destiny is to find the love of one's life, we are led to believe that Jack found his in The End. Kate. And if Kate's flight from justice, the other men in her life, were just casual experiences, then one could believe that Kate found her love of her life in Jack.

But she had Jack's affection at least twice, and kicked him to the curb.

And Kate was still married (to our knowledge) to the Florida policeman, Kevin Callis, the only man she made a real commitment (i.e. marriage). She had a childhood crush on her friend Tom. And during the bank robbery days, we were told that her boyfriend was Jason (but she may have just used him to get into the safety deposit vault.)

It would seem that Kate would die alone because of her tendencies to use men for short time periods, then flee the long arm of the law, or the pressures of being confined into a normal life (such as raising Aaron after her trial). If anything, Kate was destined to die alone.

And in The End, dying alone was a truth. Both Boone and Locke sat in the church alone. It is ironic that Locke preached, prayed and sought his true destiny, but he would wind up alone (even though Helen was with him in the sideways world).

Why Kate was rewarded with the company of Jack in the end may have to due more with what Jack wanted - - - subconsciously, he needed to "fix" one last thing: himself. Why he did not try to dream about reuniting with Sarah, his first love was obvious because she had moved on without him with a new husband and family. Or if Jack dreamed a quality life with an intellectual equal, then why did he not wind up with Juliet (who he had married and raised a son in the sideways world)? Because Juliet was connected with Sawyer. But Sawyer was also connected to both Cassiday (the mother of his child) and Kate. Kate may have been Jack's default because in some ways they were so alike in beating themselves down.

But that defies common sense. But most people would counter to say that love is not rational in the first place. Stranger couples are found in real life. Why not in fiction.  Maybe it was a matter of convenience to the writers.