What's a "checkmate" or "point of no return" for you in a relationship/friendship?

I generally believe in "turning the other cheek" and offering second chances, however there's a point at which I do have to just "fold" and declare the T. O. D. on a relationship or friendship. What's the point of no return for you?

What's a "checkmate" or "point of no return" for you in a relationship/friendship?
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