My Girlfriend's Best Friend

Sam and Joy had been dating for about a year and were both attending college.  Then Joy came to Sam with a strange request.  She suggested that the two of them demonstrate how to make love in front of her best friend and roommate Marcie since she was inexperienced and wanted to find out what love making was all about. This leads to some complications and before Sam knew it, Marcie had replaced Joy as his girlfriend.  Then he found out that it had been a plot all the time since Joy was planning to switch colleges since she wanted to become a doctor.  Since she didn't feel right about leaving Sam alone, she had fixed him up with her best friend.
Sam found out that Marcie was the perfect girlfriend since she ate lunch with him every day, then came over and fixed dinner for him and then spent the night, and fixed breakfast for him the next morning.  She even cleaned his apartment.  Soon they were living together.  Unlike Joy, who was pre-med and didn't have much time to spend with a boyfriend, Marcie was a business major so had plenty of time. Although Sam and Marcie got married, Joy still had strong feelings for Sam so she resurfaced later to cause problems.  Joy slowly comes back into their lives and some unexpected things happen.
This novel is intended for mature audiences.