From Oprah's article about desire in relationships

"When Odette was after Swann, he didn't notice her. And when he grew interested, she stopped caring about him," I said.

Bellagio looked up at me, his face shining, eyes flickering fire.

Emboldened, I went on. "It seems that another person's interest in us can often make our desire for them flee."

Bellagio leaned way back in his chair, kicked his foot up onto his desk, and smiled.

I don't know what gave me the courage to tell him what was on my mind, but I did. I was standing at the door, and instead of leaving I risked a confession. "Not wanting someone who wants you. It feels kind of...familiar right now."

"What? Are you living out your own Swann in Love?" he said. I knew he wasn't going to let it go.

"Actually, it's my boyfriend. You met him two weeks ago at the play." I blushed fiercely. I knew I wasn't being clear. "It's just that he kept leaning against me.... he's..."

"Always around? Too attentive?" said Bellagio.

He'd nailed it. "How did you guess?"

"Law of nature, of desire, if you will," said Bellagio. "He wants you, so you don't want him."

This is what I call the Conquistador Mentality. You want what you can't have. Once you have it, there game is over and you're ready for a new conquest.
This happened to me with my ex. He had to have me, but once we married, he no longer had any interest in me.