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At the end, he calls Goon back and apologizes for insulting him and even agrees to start calling him Rocky.
When he realizes his love for Layla, he buys her a heart-shaped cookie. Then he turns to a random customer in the diner and asks if he has a girlfriend. He confirms that he does, so Billy buys him one too, to take home.
The final shot of Billy in Layla's arms.
While it happens gradually and subtly, Layla agreeing to stay and look after Billy is also quite heartwarming, especially when she more or less admits her love for him.