Cosby describes their relationship as romantic. But her lawyers say he was only a mentor and trusted friend.
Their relationship will no doubt be explored in depth if a judge Tuesday allows the 12-year-old case to trial.
Defense lawyers say the 78-year-old Cosby had a deal with authorities that he should testify in Andrea Constand's lawsuit because he would never be charged.
Ex-Montgomery County District Attorney Bruce Castor will testify for the defense Tuesday.
The current prosecutor, Kevin Steele, says he has no evidence of any immunity deal.