butterfly days

[keannu]

Judging from "fascinated, don't you worry, will we see", is it possible that she liked him before? What do you mean by butterfly days ? One's prime time or riding high days?

Hearts and Hands by O. Henry​

The girl's eyes, fascinated, went back, widening a little, to rest upon the glittering handcuffs.​

"Don't you worry about them, miss," said the other man. "All marshals handcuff themselves to their prisoners to keep them from getting away. Mr. Easton knows his business."​

"Will we see you again soon in Washington?" asked the girl.​

"Not soon, I think," said Easton. "My butterfly days are over, I fear."​

 

[SoothingDave]

It's not a common expression. Perhaps they shared some time in the past, perhaps a day spent chasing butterflies.