The following chapters from The Wiley Handbook of Sex Therapy may be helpful as you decide on which model to use for your assignment (or locate sources outside of these for the assignment).
The book can be accessed directly from Ebook Central here: https://search.ebscohost.com/login.aspx?direct=true&AuthType=sso&db=cat01034a&AN=nu.EBC4825473&site=eds-live&scope=site&custid=natuniv (search: The Wiley Handbook of Sex Therapy)