William Finnegan, 59, told a jury that despite having taken a vow of celibacy, he got married more than a decade ago and kept it a secret from both the church and his parishioners.
Finnegan, also known as “Father Bill”, was parish priest at St Clare's RC Church in Fagley, Bradford, West Yorkshire, when the alleged sexual assault happened.
He denies sexually assaulting the teenager on Easter Sunday last year by touching her bottom and forcefully kissing her, and is standing trial at Bradford Crown Court.
His barrister, Jeremy Hill-Baker, told the jury: "You may be thinking that he is only human, that Father Bill, as a Catholic priest, has taken a vow of celibacy, condemning himself to a single and lonely life filled with perhaps an underlying sexual frustration because, let's face it, it is not a natural state for a human to be in.
"It would be understandable for you to be thinking, 'Well, perhaps it just got the best of him with that 17-year-old'."
But he told jurors they would hear evidence from both Finnegan and his wife, Beverley Dawson.
The lawyer went on: "No, you didn't mis-hear me. His wife. He and Beverley Dawson secretly married abroad in September 1999.
"So deeply in love was he that he was prepared to ignore the Catholic Church's ban on marriage, a secret which has been kept from almost everyone until now.
"Whatever the outcome of this case, his ministry as a Catholic priest is well and truly over."
The court heard that Finnegan met Mrs Dawson, a mother-of-two, when he was a priest in Castleford, West Yorkshire, and she was one of his parishioners.
After her previous marriage broke down, they fell in love and travelled to Cyprus to wed in a civil ceremony and only disclosed their marriage to close friends and family.
Mr Hill-Baker said: "Far from being celibate, they enjoyed a full and active sex life."
The Recorder of Bradford, Judge Roger Thomas QC, told Finnegan before he gave his evidence: "Your public announcement of this today is news to everyone?"
Finnegan replied: "It is, and I will be dealt with."
The judge asked him if he had been suspended since the allegation of sexual assault arose.
The priest replied: "I have been suspended and simply ignored."
Finnegan told the jury it was the girl who had made approaches to him, adding: "She tiptoed towards me, placed her hands on my waist and kissed me on the lips."
He said he pushed the girl away and told her: “That's not to happen.”
Giving evidence, Mrs Dawson said she and her husband had never permanently lived together but saw each other regularly, had a sexual relationship and went on holidays together.
She said each week after he finished his church service on Sunday he would visit her, then go back to work on Tuesday.
She said on the day in question, Finnegan had phoned her and told her he had been kissed by the teenage girl. "He was shocked," she said.
The trial continues.
