I have plenty of ideas but there is one which I like most. When I read erotic stories, I want hot sex and with bullies' stories, if it's from the son's POV, the sex is indirect. It's hearing through the walls or from a phone.
So my idea is to have a son read his mother's diary. At the start, we learn the mother is gone with a message "I'm not coming back" left on the kitchen table. Parents are divorced (or the father is dead) so it was just the mother and son in the house. The son wants to know what happened to his mother. He noticed the changes from the past six months. She dressed more sexily, she was gone more often and the previous well kept house wasn't anymore. He goes through his mother's belonging and finds her diary.
At first it's all about the stress from work, raising a child on her own and her inability to find a good man. Then it changes. He reads how his mother scheduled an appointment with his bully's parents after her son came home with a bruise. The parents were there but the bully was. He talks to her how he is better than her son, how much of a real man he is and how hot she is. He half seduced and half forced himself into her. The son is shocked by this revelation and more shocked when he reads that his mother came duing the rough sexual encounter. She is horrified by the fact that her body enjoyed being brutally fucked while her mind denied the pleasure.
After that the diary goes about how she couldn't stop thinking about the bully and how she slowly submitted to him. The sex becomes nastier and nastier as she lost herself in the relationship. She even quitted her job to spend more time with the bully and used her savings and her son's college founds to pay for everything the bully wanted. As the son reads the diary, he also remembers some events of the diary from his POV. Like a discussion between his bully and his friends about his new bitch and the new watch she bought him. Or when his mother missed his birthday because of work but the diary read she was gangbanged by his bully and his friends.
With this setup, you have both POVs to have the best experience. The hot sex and the degradation thanks to the mother's POV and the son's humiliation thanks to his POVs.
You can even have the son read the diaries for weeks and jack off to it. You see how he is changing from this as he begins to imagine his crush and bullies fucking until he reads that it actually happened.