The female officer said Gary Cryans, a constable with Strath-clyde Police, drove her home from a night out in June 2009, because she was so drunk.
But the constable said as she woke up, not knowing where she was, he climbed on top of her.
The pair also exchan-ged text messages, the court heard, including him telling her he had a "passion" for her.
The woman, who cannot be named, was giving evidence at the trial of constable Cryans, 51, at Glasgow Sheriff Court. He faces nine charges of sexual assault and one of breach of the peace.
She told the jury after being on a night out in Glasgow city centre he offered to take her home because she was so drunk and that her friend went with her.The court was told that when the car began to move the officer soon fell asleep. But, she said, when she woke up her friend was gone.
The woman alleges that at a party later that month, where the pair were both staying overnight, he pulled her shorts down as she slept, waking her up.
The court heard that the pair often sent texts to each other.
The witness accepted she sent him a text when he was on holiday in July 2009 and told him she wished she was sunning herself with him.
She also told him she wanted them to get on a plane together.
The constable told the jury she had no explanation for why she was sending those sorts of text messages and said it was "easier to go along with the way Gary thought about things".
Shelagh McCall, defending, put to the witness that she kissed his neck during the night out that he took her home, but this was denied.
Cryans, of Uddingston, denies the charges, dating from between March and August 2008, June 2009 and between September and November 2009. He has lodged a special defence of consent on four charges of assault.
The trial continues.