It's a Long Story

Meaning/Usage: Used when you don't want to talk about something, if it is difficult to talk about; or if it is hard to explain

Explanation: This expression is straightforward, but can be used to say you don't want to talk about it, even if the story is not very long.

"I know you want to know what happened but it's a long story."
"It's a long story about what happened between us."
"We used to be friends but it's a long story."

A. "Hey there's Tim. Didn't you guys used to be good friends?"
B. "Yes, we were friends a few years ago but not anymore."
A. "Why, what happened?"
B. "It's a long story."

Other Common Sentences

"It's hard to explain."
"It will take a while to explain."