Faculty Sex by Sam Hinton

From the back:

College sin...

Amy Lovell, sculptor, was a bohemian in the sedate world of a college community. Her professor husband spurned her love for a coed mistress. By day, he was prim, proper... at night, when he wasn't checking up on pantie raides, he was dressing his wife in weird exotic undies.

Amy was a highly passionate wife with no love. She turned to the eager, hot bodies of students, professors... male students posed nude for her 'rewards'. She took her husband's coed mistress to bed to keep her marriage and in this twisted wya, found out why her husband yearned for the young girl just as she, too, yearned for the young girl's body.