Answer: Below
Step-by-step explanation:
If I recall correctly, Two-Bit was afraid that Ponyboy was going to become too hard. What assuages him is Ponyboy assuring Two-Bit that he would have never used that broken bottle on the Socs.
It's related because the Robert Frost poem is hinting that the most beautiful things are in the beginning, but they won't be there forever. Ponyboy's innocent nature is the gold in this context.