Mark catches his sister red-handed (well, sort of), which leads to her giving him some quite unusual sisterly advice. (Written a while back under a different pen name, but still pretty good IMHO.)
Samuel Feldman still lives with his mother, who is closer in age due to how young she was when she bore him. However, he's not a loser. He's a history teacher and he has a girlfriend that his mother seems to dislike, as well as a gay ex-boyfriend. Things change on Election Day, starting with a fight with Mom.
"Hannah sat upright on top of her eighteen-year-old brother and swept her sweaty hair away from her face. Cum leaked from her sixteen-year-old pussy down over his exhausted dick and emptied balls." --- His sister falls in love with her brother and wants to be close... Really close!