There's Something About Mary Lynn (S03E10)

Mary Lynn, a single mother, finds herself drawn to Edmonds, a man recently divorced. However, she soon senses that there’s something off about his 10-year-old son, Tennent. Unbeknownst to her, Tennent harbors an intense desire not just to befriend Mary Lynn, but to completely emulate her. This unsettling fixation sparks the start of a chilling 22-year obsession that will have far-reaching and destructive effects on both families involved.