Mr Evans, 56, fell for the bi-sexual younger man, according to his girlfriend, his trial at Preston Crown Court heard.
The former deputy speaker of the House of Commons, is accused of assaulting the young man at his home in 2009, the year before Mr Evans publicly admitted he was gay.
The complainant's then girlfriend said she thought the MP was in love with her boyfriend.
The young man told the court after a drinking session he awoke on Mr Evans' settee to find the MP's hand inside his boxer shorts. He pushed the MP on the floor and demanded an explanation before making phone calls to his girlfriend for help to get away.
The woman, told the jury her ex-boyfriend was "in disbelief" and "really angry." She added: "I knew he (Evans) was a attracted to him.
"I knew there was frequent, in my view, what I would consider inappropriate contact between them. It's true, I absolutely formed the opinion he had fallen in love with my boyfriend."
Mr Evans denies one rape, two indecent assaults and sexual assaults.
The trial continues on Monday.