Dorothy Plunk of course was the girl that Homer had fallen in love with very early on in his high school career. He studied with her and fell ever more deeply in love with her as time went on but was broken hearted when his brother took her out. From that point on he vowed not to care for her anymore, but was generally unsuccessful.
He writes that she (the girl whose name isn't Dorothy Plunk but who the character was based on) went on to marry a wonderful guy and raise a couple of wonderful daughters. He writes that they are still friends and that when he saw her again 25 years after their high school graduation, he still loved her.