Because there is no blood relation, the stepmother and son get excited about and have a relationship with just the body of someone who is only family in name. Ignoring her useless husband's limp dick, the lewd stepmother uses her young son's sturdy and hard cock as a 'tool' to satisfy her sexual desires. When her body heats up, she immediately sucks on her son's meat rod, using her vaginal depths to constrict and provoke internal ejaculation with intense hip movements.
