SEX

"I believe that sex is one of the most beautiful, natural, wholesome things that money can buy." - - - Steve Martin.

Sex was an element in LOST but it was not truly associated with love.

Kate and Sawyer's affairs were more animal lust than true, deep passion. It was the spark of danger between people running away from their problems.

Kate and Jack's romance was more a convenience (in order to keep Aaron in LA) than a deep bond of attraction, friendship, trust and mutual respect. They may have loved each other but they were not in love with each other. 

Kate used sex as a manipulation of men to do what she needed to do to maintain her freedom.

Sawyer used sex as a means of conveying trust to one of his con artist victims.

Jack appeared to have a cold distance to sex and romance, perhaps because of the chill between his parents while he grew up. He was passionate with Sarah, his first wife, not because of her but because he promised her a miracle. She was more a trophy of his success than a real life partner. Sarah quickly understood this through Jack's jealousy of his father so she divorced Jack.

Sun quickly felt that sex with Jin was more a marital obligation than true love. Her feeling for her husband quickly changed when Jin began to change into the mirror image of her business oriented father. 

Claire and Shannon used sex as a means of finding comfort and support from men. They chose interloper boyfriends than real permanent bonds. Both paid the price for looking for an easy path to acceptance. 

Then there were a large group of sexless loners including Hurley, Daniel and Charlie. They were looking for a special woman, but could not overcome their own insecurities until they reached the island. But events took their potential lovers away from them until the reunion in the after life.

Many fans believed the only true love story in the series was the relationship between Desmond and Penny. The star-crossed lovers went back and forth; questioning their own feelings and self-worth; longing for each other when Widmore put himself between them. Then, the long search to be reunited after Desmond was lost at seas. When they were reunited, they pledged themselves to each other. Their sexual union brought forth a true family, which Desmond vowed to protect from Widmore. And it was Desmond's love for Penny that broke the barriers in the sideways world so every major character could remember their closest island bonds. It was that break that caused humanity to prevail in the sideways world.