I don't own Star Trek or any of it's characters
Data considered himself to be a logical being. He always did the logical thing, being a machine. It was how he was programmed. His loyalty was not to the federation, or to his friends. It was to the ideals his creator had programmed in him. There were only two times in his life that he had defied logic and done what he... wanted to do. This wanting had only happened twice. The first time had no serious consequences- he had no feelings, so therefore was perfectly fine when she said, "This never happened". He credited Tasha for making him have the closest thing he could experience to feelings. For this, she would always have a special place in his memory engrams. Until he got his emotion chip, and reliving the experience became painful for him.
The second time was far more powerful, far more potent. He wasn't being offered just sex. He was being offered what he'd always wanted. Humanity. Flesh and blood. Physical sensation. The possibility of feeling actual pleasure. She was so seductive, so passionate. He was never able to tell if it was an act or if she actually wanted him. When she asked him how long it had been since he experienced sexual pleasure and he answered,
"Eight years, seven months, sixteen days, four minutes, twenty-two-" and then she kissed him with a burning passion. Eight years, seven months, sixteen day, four minutes, and twenty-two seconds of friendship, love, service, loyalty- he considered giving it all up. He considered betraying his family. But he didn't. He chose the logical thing, but this time it wasn't based on logic. It was based on his gained human experiences, his... feelings. He can very clearly recall his conversation with the Captain just after the Borg Queen was dead.
"For a time, I was tempted by her offer."
"How long a time? "
"0.68 seconds sir. For an android, that is nearly an eternity."
Not much can happen in 0.68 seconds. An eyelid can blink, you heart can half-beat. But in 0.68 seconds, an android determined the fate of humanity. And this made him more human than anyone.