S18E08 The Haw-Hawed Couple
Nelson declares Bart his best friend after Bart is the only child to turn up for his birthday party. Initially there are fringe benefits but then Nelson becomes jealous when Bart plays with Milhouse. Things come to a head on a field trip when the boys are trapped in a flooded cave- before reverting to normal. Homer becomes obsessed with Lisa's fantasy heroine Angelina Button which he reads to her but becomes Lisa's own hero after changing the ending of a storyline to make her happy.